DIY - Build and install a Bussmann RTMR Fuse/Relay Block

Part 1 - Introduction



This is Part 1 in a series of tutorials that will show you how to build a Bussmann RTMR fuse/relay block. If you’re not familiar with this product, it’s a simple waterproof enclosure that allows you to connect accessories on your vehicle through relays and/or fuses.

After reading this tutorial, you will have the knowledge and skills to build one of the above fuse blocks that you can then install in your vehicle. This will end up being the foundation that you can then add accessories to such as lights, compressors, radios, and more.

This part will introduce you to the Bussmann RTMR and hopefully answer some questions. By the end of this part, you should have a better understanding of what this device is capable of and if it’s something that you need. I’ll explain many details, but let me first outline the upcoming parts in this series.

• Part 1 – Introduction
• Part 2 – Parts
• Part 3 – Tools and Techniques
• Part 4 – Wiring and Schematics
• Part 5 – Building The RTMR
• Part 6 – Installation

Before proceeding, a word of warning. I take no responsibility for damage, accidents, or injuries resulting from the fabrication or installation of any electrical modifications to your vehicle. You do so at your own risk.

What is the Bussmann RTMR?

In simple terms, the Bussmann RTMR is a fuse/relay block. Although the manufacturer, Cooper Industries, which is part of Eaton, calls it a Power Distribution Module. This serves as a central connection point for various accessories in your vehicle. The device consists of fuses and relays to accommodate switched and non-switched accessories.

There is additional info at Cooper Industries website regarding the RTMR, most specifically within the datasheet. We’ll take a look at the datasheet as we proceed through this tutorial. For now, here’s the specific webpage for the Bussmann RTMR 15300 Series Power Distribution Module.

The RTMR is an acronym for “Rear Terminal Mini Fuse and Relay”. What this means is that the device allows you to insert terminals into the rear side with mini fuses and relays inserted into the front. It’s a weather tight enclosure(IP66), when used with appropriate cover, cable seals and cavity plugs. Additionally, there are several models with various configurations of internal electrical bussing. Out of the available models, there are really only two that I feel are the most versatile. I’ll detail the differences in Part 2 – Parts.

Why would I want one?

The primary reason to make one of these enclosures is if you want to add accessories to your vehicle, such as lights, compressors, radios, water pumps, etc. Of course, all of this is possible without using an enclosure such as the RTMR. However, as you continue to add accessories to your vehicle, the organization of the wiring can quickly get out of hand. Take a look at the following image. This is a vehicle with poor electrical organization. Although connected directly to the battery, the wires are all over the place, and it’s a potential fire hazard. The RTMR will clean this up nicely.


Photo by @Shmellmopwho . He has since cleaned his wiring up with an auxilliary fuse block and circuit breaker.

Besides clean wiring, using an RTMR prevents you from having to branch off the OEM stock fuse block using fuse-taps. Of course this can be done, but you have to be very careful that you don’t overload a circuit, creating another potential fire hazard.

And finally, another safety feature of the RTMR is the use of relays. By routing the high-current accessory through a relay instead of directly through a switch, you’re minimizing the amount of current at your fingertips. If you don’t quite understand how relays work, I’ll get into more detail in Part 4 – Wiring and Schematics.

Why build it myself? Can’t I just buy one already made?

There’s an old proverb, “Give a man a fish, and he’ll eat for a day. Teach a man to fish, and he’ll eat for a lifetime.” I definitely fall into the latter camp, and I encourage you to do the same. By taking the time to read this tutorial and learning how this box is put together, you’ll learn a lot of the basics about electricity as well as how all of your accessories are installed in your vehicle. This will serve you well, especially if you’re out on the trail offroading and you need to trouble-shoot a problem. Additionally, you’ll save a few dollars over the long haul when it comes to installation of additional accessories. With the RTMR in place, your foundation will be setup. Adding a new accessory is practically plug-and-play.

Building a RTMR fuse/relay block is not beyond your ability. Anyone who puts in the time can build one. If you like working with your hands and solving problems, you can do this. If you’re willing to make mistakes and learn from them, you can do this. If you want to be self-sufficient, you can do this. Building one of these fuse blocks is not difficult. It just takes a bit of time and patience.

However, if you’re uncertain, hesitant, unskilled or impatient to take on this project yourself, you have options. Several vendors are selling this enclosure pre-built or selling something similar. Here’s a list I’ve gathered together.

• SPOD
• Trail Toys NSA Switch Panel
• PMA 4×4
• Painless Performance
• Blue Sea (fuse blocks only, no relays)
• Bussmann RTMR from I8Mud.com forum member
• Bussmann RTMR from Tacoma World forum member, Yotamac

In Part 2 – Parts, I’ll outline all of the parts needed to build the RTMR.

 

Part 2 - Parts



This is Part 2 in an on-going series of tutorials that will teach you how to build a Bussmann RTMR fuse/relay block for your vehicle. Part 1 was simply an introduction, but in this part I will get into the specifics of the parts needed to build this enclosure. There is a lot to cover with many specific details.

As a broad overview, here is a list of parts that you’ll need to buy. Some of these are self explanatory, yet others might be a bit foreign to you. As I detail each part, I’ll provide part numbers as well as where they can be sourced. Then at the end, I’ll reiterate with a complete itemized list of all the parts needed.

• Bussmann RTMR fuse block
• Terminals
• Cable seals
• Cavity plugs
• Wire
• Metri-pack Connectors
• Weather-pack Connectors
• Fuse and/or circuit breakers
• Relays
• Wire Loom
• Heat shrink
• Mounting bracket
• Busbars
• Heat shrink ring terminals
• Copper crimp lugs
• Switches
• Switch Panel
• Switch Blank
• Fuse Tap
• Wire tap
• Molex Mini-Fit Jr. connectors
• Molex Mini-Fit Jr. terminals

And as a reminder, I take no responsibility for damage, accidents, or injuries resulting from the fabrication or installation of any electrical modifications to your vehicle. You do so at your own risk.

Bussmann RTMR Fuse/Relay Block

Let’s begin with the Bussmann RTMR fuse block itself. What is it? Where can you get it? What differences are there between model numbers?




The Bussmann RTMR is made by Cooper Industries, and we will be using the Series 15300 RTMR. By looking at the datasheet for the box, you might quickly be overwhelmed with all the options. My hope is that I can simplify it for you. Let’s start with the Part Numbering System. Using the following table from the datasheet, we’ll be able to determine exactly what type of box to order.




As an example, let’s use the model number, 15303-2-2-4, and decipher the values from left to right:

• 15303 -2 – 2 – 4 : These four number will never change for this product.
• 15303 -2 – 2 – 4 : Mounting – This specifies what type of mounting screw is inserted into each of the four corners of the box. In this example, the specification is #10-32 Insert (English). You will find that this is the most common option in the USA. In fact, finding the metric option is quite difficult.
• 15303 – 2 – 2 – 4 : Base Options – This specifies the configuration of the box, which can include whether it holds relays and/or fuses. Additionally, it defines if there is any internal bussing. In this example, the specification is Micro Relay Base (For 5 Micro Relays W/ 10 Fuses/C.B.). So this means that this configuration is setup for 5 micro relays and 10 fuses or circuit breakers. It’s also implying by default that there are two internal busses. One is for the fuses, and the other is for the relays.
• 15303 – 2 – 2 – 4 : Hardware Options – This specifies what hardware options are included with the box, such as whether bus stud nuts are included, attached, and whether stud caps are included. In our example, the specification is Nuts (Shipped Assembled), which means nuts are included on the bus studs, attached, and without stud caps.
• 15303 – 2 – 2 – 4 : Cover Options – This specifies whether a cover is included with the enclosure. In order to make it waterproof, you definitely want a cover. In our example, the specification is Relay/c.b. Cover, which means a tall cover is included to allow for circuit breakers.

With the part numbering system in mind, study the Base Options in the following image from the datasheet in more detail.




In my opinion, there are only two configurations that should really be considered for an auxiliary fuse/relay block. Having an internal bus for the fuses is very advantageous, because this allows a single power source to be connected to the RTMR that supplies power to each fuse. Therefore, our choices are limited to three configurations: 1530X-1-X-X, 1530X-2-X-X, and 1530X-5-X-X. Additionally, I want to be able to use relays in addition to fuses, so that eliminates 1530X-1-X-X from our three choices. Two remain, either of which will work, 1530X-2-X-X and 1530X-5-X-X.

• 15303-2-2-4 – This box has two internal busses, one for fuses and another for the relays. Bus stud nuts are included and attached. A tall cover is included to account for circuit breakers.
  
• 15303-5-2-4 – This box has one internal bus for the fuses only. Bus stud nuts are included and attached. A tall cover is included to account for circuit breakers.

There will be differences in how things are wired between these two versions, but this tutorial focuses on 15303-2-2-4. I’ll detail the connections in Part 4 – Wiring and Schematics.

Part used in this tutorial:

• Bussmann 15303-2-2-4

Where to buy:

• Waytek Wire

Metri-Pack Terminals

The Bussmann RTMR uses Metri-Pack 280 Series terminals and seals, which are made by Delphi Automotive PLC. There are two types of terminals offered in the Metri-Pack 280 Series, tanged and tangless. The RTMR specifically uses tangless sealed female terminals.

If you look at page 84 in the Metri-Pack catalog at Delphi, you’ll find a list of tangless female sealed terminals:

Metri-Pack 280 Tangless Sealed Female Terminals

Part # -- AWG Size
12110853 -- 12-10 AWG
12110845 -- 14-12 AWG
12129409 -- 16-14 AWG
12110847 -- 18-16 AWG
12110846 -- 22-20 AWG






Later on, I’ll be using Metri-Pack connectors when making accessory cables that connect the Bussmann RTMR. These connectors, however, use tanged sealed female and male terminals. If you look at page 84 in the Metri-Pack catalog at Delphi, you’ll find a list of tanged female sealed terminals:

Metri-Pack 280 Tanged Sealed Female Terminals

Part # -- Typical Wire AWG Size
12077413 -- 10-12 AWG
12129493 -- 12-14 AWG
12077411 -- 16-18 AWG
12084201 -- 20-22 AWG
12176387 -- 10-12 AWG
12176388 -- 12-14 AWG
12176389 -- 16-18 AWG

And then on page 85 in the Metri-Pack catalog at Delphi, you’ll find a list of tanged male sealed terminals.

Metri-Pack 280 Tanged Sealed Male Terminals

Part # -- Typical Wire AWG Size
12048254 -- 10-12 AWG
12129497 -- 12-14 AWG
12048159 -- 16-18 AWG
12124977 -- 20-22 AWG



Parts used in this tutorial:

• Metri-Pack 280 Sealed Tangless Female 12-10 AWG – 12110853
• Metri-Pack 280 Sealed Tangless Female 18-16 AWG – 12110847
• Metri-Pack 280 Sealed Tanged Female 12-10 AWG – 12077413

Where to buy:

• Metri-Pack 280 Sealed Tangless Female 12-10 AWG – 12110853: Mouser
• Metri-Pack 280 Sealed Tangless Female 18-16 AWG – 12110847: Waytek Wire
• Metri-Pack 280 Sealed Tanged Female 12-10 AWG – 12077413: Waytek Wire

Tip:

When making your parts purchase, you may want to buy terminals for other gauge sizes. These would be used in the Metri-Pack connectors for your accessories. Suggested parts to purchase would be:

• Metri-Pack 280 Sealed Tanged Female 14-12 AWG – 12129493: Waytek Wire
• Metri-Pack 280 Sealed Tanged Female 18-16 AWG – 12077411: Waytek Wire
• Metri-Pack 280 Sealed Tanged Male 12-10 AWG – 12048254: Waytek Wire
• Metri-Pack 280 Sealed Tanged Male 14-12 AWG – 12129497: Waytek Wire
• Metri-Pack 280 Sealed Tanged Male 18-16 AWG – 12048159: Waytek Wire

Weather-Pack Terminals


I’ll be using a Weather-Pack connector for the switch wiring harness. These use different terminals than the Bussmann RTMR and Metri-Pack connectors.

Weather-Pack Female Terminals

Part # -- Typical Wire AWG Size
12124581 -- 12-14 AWG
12124580 -- 16-14 AWG
12089188 -- 18-16 AWG
12020801 -- 22-20 AWG


Weather-Pack Male Terminals

Part # -- Typical Wire AWG Size
12124587 -- 14-12 AWG
12124582 -- 16-14 AWG
12089040 -- 18-16 AWG
12089307 -- 22-20 AWG

Parts used in this tutorial:

• Weather-Pack Female 20-18 AWG – 12089188
  
• Weather-Pack Male 20-18 AWG – 12089040

Where to buy:

• Weather-Pack Female 20-18 AWG – 12089188: Waytek Wire
• Weather-Pack Male 20-18 AWG – 12089040: Waytek Wire

Cable Seals

Within the Metri-Pack 280 Series of weatherproof connectors, the system works to keep the water and contaminants out of the electrical connection by using rubber wire seals. If you look at page 84 in the Metri-Pack catalog at Delphi, you’ll find a list of cable seals. Out of list, the Tan and Purple are not readily available so are not typically used.

Metri-Pack 280 Cable Seals

Part # -- AWG Size, Color
12015193 / 15324981 --12 AWG, Blue
12010293 / 15324980 -- 14-16 AWG, Light Gray
12015323 / 15324982 -- 18-20 AWG, Green
12041351 -- 18-20 AWG, Tan
12089679 -- 20-24 AWG, Purple
12015899 / 15324983 -- 20-22 AWG, Red


For my project, I purchased the blue and green seals.



Parts used in this tutorial:

• Metri-Pack 280 Cable Seals Blue 12 AWG – 12015193 / 15324981
  
• Metri-Pack 280 Cable Seals Green 20-18 AWG – 12015323 / 15324982

Where to buy:

• Metri-Pack 280 Cable Seals Blue 12 AWG – 12015193 / 15324981: Waytek Wire
• Metri-Pack 280 Cable Seals Green 20-18 AWG – 12015323 / 15324982: Waytek Wire

Tip:

When making your parts purchase, you may want to buy the following part to accommodate 16-14 AWG wire:

• Metri-Pack 280 Cable Seas Light Gray 16-14 AWG – 12010293 / 15324980: Waytek Wire

Cavity Plugs

If you’re not using a particular cavity in the Bussmann RTMR or even on a Metri-Pack or Weather-Pack connector, you need to seal it with a Cavity Plug. There is only one part available and needed within the Metri-Pack 280 Series to seal unused female and male cavities:

Metri-Pack 280 Cavity Plug

Part # -- Color
12010300 -- Green

Part used in this tutorial:

• Metri-Pack 280 Cavity Plugs – 12010300

Where to buy:

• Metri-Pack 280 Cavity Plugs – 12010300: Waytek Wire

Wire

For automotive wiring, there are three typical wire types that are used: SXL, GXL, and TXL. They have many of the same features, including high temperature ratings, great flexibility and cross-linked polyethylene insulation. The main difference between them is insulation wall thickness. SXL is standard thickness, GXL is thin wall, and TXL is extra-thin wall.




SXL

SXL wire is recommended for use in high temperature environments where high heat resistance is required as per SAE J-1128. SXL wire is frequently found in engine compartments, trucks, tractors, boats, buses, and general applications where high durability coupled with high heat resistance is a requirement.

• Conductor: Bare Copper
• Insulation: Cross-Linked Polyethylene (XLPE)
• Recommended Temperature Range: -51°C to +125°C.
• Voltage Rating: 50 volts
• Ford Specification: Ford (M1L-85A)
• Chrysler Specification: Chrysler (MS-5919)
• SAE Specification: SAE J-1128

GXL

GXL wire is recommended for use in high temperature environments where high heat resistance is required as per SAE J-1128. GXL wire is frequently found in engine compartments, trucks, tractors, boats, buses, and general applications where high durability coupled with high heat resistance is a requirement.

• Conductor: Bare Copper
• Insulation: Thin wall Cross-linked Polyethylene (XLPE)
• Recommended temperature range: -40C to +125C
• Recommended voltage: 50 volts
• Ford Specification: Ford (M1L-85B)
• Chrysler Specification: Chrysler (MS-8900)
• SAE Specification: SAE J-1128

TXL

TXL Wire is recommended where high temperature resistance and small overall diameter are necessary. It is found in many automotive interiors (instrument panels, interiors, etc.) TXL Wire is frequently found in cars, trucks, tractors, boats, buses, and general applications where high durability coupled with high heat resistance is a requirement.

• Conductor: Bare Copper
• Insulation: Extra thin wall Cross-linked Polyethylene (XLPE)
• Recommended temperature range: -51°C to +125°C
• Recommended voltage: 50 volts
• Ford Specification: Ford (M1L-123A)
• Chrysler Specification: Chrysler (MS-8288)
• SAE Specification: SAE J-1128

After researching, I chose to use GXL wire for this project due to it being the most commonly used and available automotive wire. More specifically, I wanted to use 18 AWG GXL wire for the switches and 10 AWG GXL wire for all of the accessory wiring to accommodate any high amperage devices. However, the overall outside diameter of 10 AWG GXL is is too big to accommodate the cable seals. Therefore, I chose to use TXL 10 AWG wire, which has Extra-Thin Wall insulation and a smaller outside diameter to accommodate the cable seals.

In the end, I purchased 18 AWG GXL wire for the switches and 10 AWG TXL wire for the accessories.

The 18 AWG GXL wire is readily available at Wire Barn, Waytek Wire, or Maney Wire as well as many other retailers.

The 10 AWG TXL wire is more difficult to find. I ended up buying it from Maney Wire, but it’s also available in 250′ rolls from Waytek Wire.

Welding Wire

To connect the main power and ground sources between your battery and the Bussmann RTMR, 4 AWG welding wire is a good choice.



Parts used in this tutorial:

• Wiring for switch harness: GXL 18 AWG blue, green, orange, white, yellow, brown, red/black
• Wiring for accessories in Bussmann RTMR: TXL 10 AWG red and black
• Wiring for main power and ground: Welding wire 4 AWG red and black

Where to buy:

• GXL 18 AWG wire: Wire Barn, Waytek Wire, or Maney Wire
• TXL 10 AWG wire: Waytek Wire, or Maney Wire
• Welding wire 4 AWG: Remy Battery

Tip:

When making your parts purchase, you may want to buy various other wire gauges to accommodate your accessories. When doing so, only red and black would be necessary.


Metri-Pack Connectors

There are several ways to connect accessories to the Bussmann RTMR. The simplest option is to directly connect each accessory to the enclosure. However, this is restrictive and inconvenient, especially if you need to remove the RTMR or attach additional accessories in the future. I chose to use Metri-Pack connectors for several reasons:

• Same system as the Bussmann RTMR
• Weatherproof
• 30 amps continuous maximum current rating

The various sealed connectors available start on page 84 in the Metri-Pack catalog at Delphi, but this family of connectors does not have a mate for every connector. I’m not going to go into great detail here. If you want to learn more, check out www.metripack.com.

I used the two-way Metri-Pack 280 Series connector. There are three components to this connector:

Female Connector Assembly: 15300027


Male Connector Assembly: 15300002


Terminal Position Assurance clip (2 required per connection, 1 each for male and female connectors): 15300014


Parts used in this tutorial:

• Metri-Pack 280 Two-Way Female Connector – 1530027:
• Metri-Pack 280 Two-Way Male Connector – 15300002
• Metri-Pack 280 Terminal Position Assurance clip – 15300014

Where to buy:

• Metri-Pack 280 Two-Way Female Connector – 1530027: Waytek Wire
• Metri-Pack 280 Two-Way Male Connector – 15300002: Waytek Wire
• Metri-Pack 280 Terminal Position Assurance clip – 15300014: Waytek Wire

Weather-Pack Connectors

Similarly to using Metri-Pack connectors for all of the accessories, I wanted a convenient way to disassemble the wiring harness to the switches. This harness will be made up of six 18 gauge wires, one for each switch and then a common ground. Unfortunately, there isn’t a six-way mating pair of connectors within the Metri-Pack family. Therefore, I used Weather-Pack sealed connectors. For more specific information regarding Weather-Pack connectors, visit www.weatherpack.com or the Weather-Pack catalog from Delphi.

There are two components to this six-way connector:

Female Assembly: 12015799


Male Assembly: 12010975


Parts used in this tutorial:

• Weather-Pack Six-Way Female Connector – 12015799
• Weather-Pack Six-Way Male Connector – 12010975

Where to buy:

• Weather-Pack Six-Way Female Connector – 12015799: Waytek Wire
• Weather-Pack Six-Way Male Connector – 12010975: Waytek Wire

Switches

The switches most typically used are V-Series sealed rocker switches made by Carling Technologies. Within the V-Series line, typical choices are Contura II & III, Contura V, and Contura X. When shopping for switches, you’re are able to choose the following characteristics:

• Dependent LED – This is a LED light that illuminates when the switch is engaged.
• Independent LED – This is a LED that illuminates when your dash lights are on.
• LED positions
• LED colors
• Switch orientation, horizontal or vertical
• printed symbols.

This allows great personalization to your project.



Parts used in this tutorial:

• Carling Technologies Contura V

Where to buy:

• OTRATTW

Switch Blank

Since the Bussmann RTMR has five relays, I plan to connect five switches, but the panel I’m using accommodates six. Therefore, I purchased a switch blank to fill in the sixth position.


Parts used in this tutorial:

• V-Series Panel Plug

Where to buy:

• OTRATTW

Switch Panel

A switch panel or holder to mount the switches in your vehicle is necessary. There are several sizes to consider depending on how many switches you want clustered together. I’m installing five switches, so the six-position switch holder fits my needs. With this switch holder, I plan to install in the the overhead console sunglass holder.


If don’t want the switches in the overhead console or it won’t accommodate the switches, you’ll need to find a location that best fits your vehicle.

If you have a Toyota Tacoma, then another option is a panel to mount the switches in the space just forward of the shifter. Iggycorp makes a great panel to fit this location that accommodates six switches, which can be purchased here.

Parts used in this tutorial:

• Six Position V-Series Switch Holder

Where to buy:

• OTRATTW

Switch Backs

When wiring switches, there are several ways to do so. A very simple way is to directly wire to the rear terminals, but the problem with this method is that if you ever need to remove the switch panel, then it’s not a simple procedure. You would have to disconnect all wires and try to remember where each one went. Therefore, other alternatives are to use switch backs or some other sort of connector.

Rear terminal housings, commonly known as switch backs, are very popular and easy to use. They’re basically a mating part that attaches to the back of the switch. Your wiring connects to the terminal housing, which then plugs into the switch. If you need to remove the switch panel, then all you do is unplug the switch backs. The other neat thing is that they come in a variety colors to help you organize your installation.

As versatile as switch backs are, I did not use them, because there was not enough space in the overhead console sunglass holder to accept the increased depth needed.


Parts used in this tutorial:

• I did not use switchbacks but wanted to let you know that these are a great option.

Where to buy:

• Black: OTRATTW
• Orange: OTRATTW
• Red: OTRATTW
• Gray: OTRATTW
• White: OTRATTW

Fuse Tap

To supply power to your switches, we will tap into the under-dash fuse panel with a fuse tap.




Parts used in this tutorial:

• ATM Add-A-Circuit, ATM Fuse Tap

Where to buy:

• $10 ATM Add-A-Fuse (Same Function as Bussmann BP/HHH) ATM Fuse Tap
  Amazon

T-Tap Wire Splice

To provide power and grounds to the lower independent LED of the switches, we will be tapping into the vehicles dash light dimmer circuit. In order to do so, this will require splicing into the OEM wiring harness.



Parts used in this tutorial:

• T-Tap Wire Splice, 22-18 AWG

Where to buy:

• Waytek Wire

Molex Mini-Fit Jr. Connectors

The one downside to using switch backs is that you need to have ample space behind the switches. So installing a switch panel in the overhead console sunglass holder, such as in my project, prohibits the use of switch backs. Therefore, I chose to use Mini-Fit Jr. connectors made by Molex. This line of connectors can host up to 24 connections at 9 amps. This project needed 9 wires to connect to the switch panel, which I’ll explain later, so I used 10-position connectors.

Male plug connectors (Molex part #39-01-3103) can be purchased at Mouser.



Female receptacle connectors (Molex part #39-01-2100) can be purchased at Mouser.



Molex Mini-Fit Jr. Terminals

Male pin terminals (Molex part #39-00-0040) can be purchased at Mouser.


Female socket terminals (Molex part #39-00-0038) can be purchased at Mouser.



Female Quick Disconnects

Insulated female quick disconnects are used to connect to the terminals on the back of the switches or switch backs. They need to be insulated, as shown. Otherwise, you severely risk an electrical hazard. Wire size to the switches will be 18 AWG, so choose the correctly sized connector, 22-18 AWG.


Parts used in this tutorial:

• 22-18 AWG Female Disconnect Red Nylon .250 X .032

Where to buy:

• Waytek Wire

Male Quick Disconnects

Insulated male quick disconnects are used in conjunction with wire splice connectors to tap into the vehicles dash lighting dimmer circuit. Wire size to the switches will be 18 AWG, so choose the correctly sized connector, 22-18 AWG.


Parts used in this tutorial:

• 22-18 AWG Mael Disconnect Red Nylon .250 X .032

Where to buy:

• Waytek Wire

Fuse and/or Circuit Breakers

The Bussmann RTMR accepts ATM Mini fuses and ATM Mini fuse circuit breakers with a 280 footprint (2.8mm). It’s a personal choice to use fuses or circuit breakers. Either will work just fine. However, if you choose to use circuit breakers, you need to purchase the RTMR with the taller cover to accommodate them.



As far as sizing goes, this is determined by the gauge of wire used.

18 AWG – 7 amps
16 AWG – 10 amps
14 AWG – 15 amps
12 AWG – 20 amps
10 AWG – 30 Amps

Parts used in this tutorial:

• This is dependent on each accessory used and will be determined by you.

Where to buy:

• At many automotive stores or online retailers such as Waytek Wire.

Relays

Depending on which version of RTMR you’re using, you need to use either ISO 280 Micro or Mini automotive relays, which have 2.8mm terminals and mate with the Metri-Pack female terminals used in the RTMR. A basic rule is if the enclosure you’ve chosen accommodates five relays, then you’ll need to buy Micro relays. Otherwise, if it only holds three, then you’ll need to purchase Mini relays. As for the RTMR enclosure I’m using in this tutorial, you want to buy ISO 280 Micro relays.

In Part 4, Wiring & Schematics, I’ll explain in more detail how a relay works and how to connect an accessory to it. For now, just understand that there are two types of relays:

• Single Pole Single Throw (SPST), Normally Open (NO)
• Single Pole Double Throw (SPDT)

The SPST relays are four-pin and the SPDT relays are five-pin. SPST relays are used to control a single circuit. When the relay is in the off position, the circuit is off. When the relay is on, the circuit is on. SPDT relays are used to control two circuits. When the relay is in the off position, one circuit is on and the other is off. When the relay is in the on position, the circuits are reversed. The first is off and the second is on.

I’m using 4-pin SPST relays in this tutorial. If you have a need for 5-pin SPDT relays, then you’ll need to make your own adjustments with regards to wiring. But it’s really easy and you’ll know how to do this after completing this tutorial. I’ll get into more detail regarding this in Part 4, Wiring & Schematics.

The relays I’ve chosen to use are made by Song Chuan and have a standard naming convention to identify them. As an example, let’s use this part number: 301-1A-C-R1



Using the above chart for reference, let’s go in order from left to right.

• 301 – 1A – C – R1 – These three numbers never change. This is the series designation
• 301 – 1A – C – R1 – This defines whether it’s a four-pin or five-pin relay. In our example, 1A indicates that it is a four-pin, Single Pole Single Throw Normally Open relay, SPST-NO.
• 301 – 1A – C – R1 – This value indicates how the relay is sealed. In our example, the relay is Flux Tight. The differences are outlined here. But basically, dust cover is not sealed, flux tight is sealed to prevent flux from entering when soldering to a circuit board, and sealed type prevents flux from entering but is also washable. Since these relays are being installed within a waterproof enclosure, the type is not that important.
• 301 – 1A – C – R1 – This value defines whether a resistor, diode, or nothing is in parallel with the internal coil. When power is disconnected from a relay, a voltage spike of hundreds of volts can develop due to the collapsing of the magnetic field across the coil. This dramatic increase in voltage can cause damage to sensitive circuits in the vehicle. Therefore, a resistor or diode is placed across the coil as a suppression circuit and is sometimes called a snubber. Both components will allow the voltage to dissipate. A resistor is more durable than a diode, so this is a common selection.

Here’s the datasheet for these relays.



Parts used in this tutorial:

• Song Chuan 301-1A-C-R1

Where to buy:

• Waytek Wire or Mouser

Wire Loom

For the switch wiring harness, I’ll be using 1/4″ expandable sleeving wire loom.


Parts used in this tutorial:

• 1/4″ expandable braided sleeving

Where to buy:

• Waytek Wire

Heat Shrink

Heat shrink is used to protect and bind wiring together. If you start researching heat shrink, you’ll find a dizzying array of options. With the Bussmann RTMR enclosure and Metri-Pack connectors, the weatherproofing doesn’t come from the heat shrink but instead the silicone cable seals. Thus, adhesive-lined heat shrink isn’t required, but I ended up using it because the adhesive helps to hold wiring and braided sleeving in place.

I used various sizes of heat shrink tubing. 3/8″ adhesive-lined, 1/2″ adhesive-lined, 3/4″ adhesive-lined, and 3/4″ clear.


Parts used in this tutorial:

• 3/8″ adhesive-lined heat shrink tubing, black – 3M EPS-300 3/8
• 1/2″ adhesive-lined heat shrink tubing, black – 3M EPS-300-1/2-BLACK-48
• 3/4″ adhesive-lined heat shrink tubing, black – 3M EPS-300- 3/4-48
• 3/4″ heat shrink tubing, clear – DSG Canusa CPX 100 0750 CLEAR

Where to buy:

• 3/8″ adhesive-lined heat shrink tubing, black – 3M EPS-300 3/8: Waytek Wire
• 1/2″ adhesive-lined heat shrink tubing, black – 3M EPS-300-1/2-BLACK-48: Waytek Wire
• 3/4″ adhesive-lined heat shrink tubing, black – 3M EPS-300- 3/4-48: Waytek Wire
• 3/4″ heat shrink tubing, clear – DSG Canusa CPX 100 0750 CLEAR: Waytek Wire

Mounting bracket

There are many ways to mount the Bussmann RTMR. You can purchase one made by Bussmann specifically for the RTMR, but you might find it very limited. You can also make one yourself out of plexiglass, steel, or aluminum. Whatever you choose, the choice is yours.

The Bussmann mounting bracket, B028-7012-0-J, is probably the most affordable and can be purchased at Waytek Wire.


The following mounting bracket is made by a Tacoma World member by the name of Yotamac that perfectly fits in a Toyota Tacoma. He makes several sizes, with and without the custom laser cut-out. So even if you don’t have a Tacoma, you may be able to mount the bracket in your vehicle somewhere. You can contact him through his message post on the Tacoma World Forum or his user profile.



Parts used in this tutorial:

• Standard Large Mounting Plate with kick-out by Yotamac

Where to buy:

• Tacoma World forum member, Yotamac

Ground Busbars

The Bussmann RTMR is configured with or without internal busses. Of the two that I recommend using, 15303-2-2-4 and 15303-5-2-4, both have an internal bus that is used to provide power to the fuses. This tutorial focuses on the RTMR that is configured with two internal busses, 15303-2-2-4.

Even though the RTMR enclosures offer internal bussing, we still need to take care of the grounds for all accessories. I chose to use two external ground busbars. One is used for five accessories attached to the relays, and the other is used for five accessories attached to fuses. I’ll get into more detail later in Part 4 – Wiring & Schematics.

The following Blue Sea Systems 5 Gang Common 100A Mini Busbar is perfect for our needs. It has five #8-32 screw terminals to attach the accessory grounds and two #10-32 stud terminals to attach the busbar to your negative battery terminal with a larger gauge wire. It’s also rated at 100A, which closely matches the rating of the internal busses of the RTMR.



Parts used in this tutorial:

• Blue Sea Systems 5 Gang Common 100A Mini Busbars

Where to buy:

• Waytek Wire or
  $12 Blue Sea Systems 2304 100 Amp Mini BusBar with 5 screws, One size, Without Cover, Black
  Amazon

Ring Terminals

To connect your ground wires from your accessories to the ground busbars mentioned above, you’ll need heat-shrink ring terminals. You’ll also need another heat-shrink ring terminal to connect the ground for the switch LEDs. I’m using heat-shrink ring terminals to protect the wiring from corrosion. You can also use standard ring terminals with adhesive-lined heat shrink if that’s what you have available.

We need ten ring terminals for the accessory to ground busbars. These are 12-10 AWG with #8 hole. We will also need one 12-10 AWG with 1/4″ hole and another 12-10 AWG with 5/16″ hole.


We need one ring terminal for the 18 AWG ground wire for the switch LEDs. Therefore, you can buy 22-18 AWG, 1/4″ hole heat shrink ring terminals from Waytek Wire, Del City, or Amazon.


Parts used in this tutorial:

• 12-10 AWG, #8 hole heat-shrink ring terminals
• 12-10 AWG, 1/4″ hole heat-shrink ring terminals
• 12-10 AWG, 5/16″ hole heat shrink ring terminals
• 22-18 AWG, 1/4″ hole heat-shrink ring terminals

Where to buy:

• 12-10 AWG, #8 hole heat-shrink ring terminals: Waytek Wire, Del City, or
  $6 Electriduct Heat Shrink Ring Terminals with Adhesive Liner 12-10AWG (Yellow) | Ring Size: 5/16" Screw - 10 Pieces
  Amazon
• 12-10 AWG, 1/4″ hole heat-shrink ring terminals: Waytek Wire, Del City, or
  $8 Electriduct Heat Shrink Ring Terminals with Adhesive Liner 12-10AWG (Yellow) | Ring Size: 1/4" Screw - 10 Pieces
  Amazon
• 12-10 AWG, 5/16″ hole heat shrink ring terminals: Waytek Wire, Del City, or
  $6 Electriduct Heat Shrink Ring Terminals with Adhesive Liner 12-10AWG (Yellow) | Ring Size: 5/16" Screw - 10 Pieces
  Amazon
• 22-18 AWG, 1/4″ hole heat-shrink ring terminals: Waytek Wire, Del City, or Amazon

Fuse Holder or Circuit Breaker

To protect the Bussmann RTMR, you will need to install a fuse or circuit breaker. The choice is up to you and tends to be a personal preference.

I used a Blue Sea ANL Fuse Holder with Insulating Cover 30- 300A, Part # 5005.


The other option is a circuit breaker: Blue Sea 285 Series Surface Mount 80A


Parts used in this tutorial:

• Blue Sea ANL Fuse Holder with Insulating Cover 30- 300A, Part # 5005

Where to buy:

• Waytek Wire or
  $26 Blue Sea Systems 5005 ANL Fuse Block with Insulating Cover, 35-300 Amp, 32V DC
  Amazon

ANL Fuses

If you choose to use an ANL Fuse Holder such as I did instead of a circuit breaker, then you need to buy 80A ANL fuses.


Parts used in this tutorial:

• 80A ANL Fuse

Where to buy:

• Waytek Wire or
  $14 Install Bay ANL80-10 - 80 Amp ANL Fuses (10 Pack)
  Amazon

Copper Crimp Lugs

As mentioned earlier, I chose 4 AWG welding wire to connect the Bussmann RTMR to the battery positive and ground. For the studs on the Bussmann RTMR, you’ll need lugs with a 5/16″ hole. The studs on the Blue Sea busbars, are #10-32, so the smallest available lug for 4 AWG that I could find was 1/4″ hole. Depending on your specific setup, you may need to get lugs with a 3/8″ hole or even 1/2″ hole.



Parts used in this tutorial:

• To connect to battery: select depending on your setup
• To connect to ANL Fuse holder: 4 AWG with 5/16″ hole
• To connect to Bussmann RTMR: 4 AWG with 5/16″ hole
• To connect to external busbars: 4 AWG with 1/4″ hole

Where to buy:

• Remy Battery

Itemized parts list

This article has outlined all of the necessary parts required to build an enclosure. To summarize, I’ve included the following list with part numbers, links to where each part can be purchased, and quantities needed. When ordering, keep in mind that many parts require a minimum number to order. This isn’t a bad thing, because mistakes will be made. Therefore, it’s beneficial to have extras available.

Bussmann RTMR 15303-2-2-4

• Where to buy: Waytek Wire
• Quantity: 1

Metri-Pack 280 Sealed Tangless Female 12-10 AWG terminals – 12110853

• Where to buy: Mouser
• Quantity: 20

Metri-Pack 280 Sealed Tangless Female 18-16 AWG terminals – 12110847

• Where to buy: Waytek Wire
• Quantity: 5 (minimum purchase will apply)

Metri-Pack 280 Sealed Tanged Female 12-10 AWG terminals – 12077413

• Where to buy: Waytek Wire
• Quantity: 20 (minimum purchase will apply)

Metri-Pack 280 Cable Seals Blue 12 AWG – 12015193 / 15324981

• Where to buy: Waytek Wire
• Quantity: 40 (minimum purchase will apply)

Metri-Pack 280 Cable Seals Green 20-18 AWG – 12015323 / 15324982

• Where to buy: Waytek Wire
• Quantity: 17 (minimum purchase will apply)

Metri-Pack 280 Cavity Plugs – 12010300

• Where to buy: Waytek Wire
• Quantity: 10 (minimum purchase will apply)

Metri-Pack 280 Two-Way Female Connector – 15300027

• Where to buy: Waytek Wire
• Quantity: 10 (Additional if using connectors at accessories.)

Metri-Pack 280 Two-Way Male Connector – 15300002

• Where to buy: Waytek Wire
• Quantity: 10 (Additional if using connectors at accessories.)

Metri-Pack 280 Terminal Position Assurance clip – 15300014

• Where to buy: Waytek Wire
• Quantity: 20 (Additional if using connectors at accessories.)

Weather-Pack Female 20-18 AWG terminal – 12089188

• Where to buy: Waytek Wire
• Quantity: 6 (minimum purchase will apply)

Weather-Pack Male 20-18 AWG terminal – 12089040

• Where to buy: Waytek Wire
• Quantity: 6 (minimum purchase will apply)

Weather-Pack Six-Way Female Connector – 12015799

• Where to buy: Waytek Wire
• Quantity: 1

Weather-Pack Six-Way Male Connector – 12010975

• Where to buy: Waytek Wire
• Quantity: 1

GXL 18 AWG wire

• Where to buy: Wire Barn, Waytek Wire, or Maney Wire
• Colors: black, blue, brown, green, orange, red, red/black, white, yellow
• Quantity : about 10′ each color (minimum purchase will apply)

TXL 10 AWG wire

• Where to buy: Waytek Wire, or Maney Wire
• Colors: black, red
• Quantity: less then 5′ each color (minimum purchase will apply)

Welding wire 4 AWG

• Where to buy: Remy Battery
• Colors: black, red
• Quantity: dependent on your installation

Song Chuan 301-1A-C-R1 four-pin relays

• Where to buy: Waytek Wire or Mouser
• Quantity: 5

Blue Sea Systems 5 Gang Common 100A Mini Busbars

• Where to buy: Waytek Wire or Amazon
• Quantity: 2

1/4″ braided sleeving wire loom

• Where to buy: Waytek Wire
• Quantity: about 10′ (minimum purchase will apply)

3/8″ adhesive-lined heat shrink tubing, black – 3M EPS-300 3/8

• Where to buy: Waytek Wire
• Quantity: one 48″ stick (minimum purchase will apply)

1/2″ adhesive-lined heat shrink tubing, black – 3M EPS-300-1/2-BLACK-48

• Where to buy: Waytek Wire
• Quantity: two 48″ stick (minimum purchase will apply)

3/4″ adhesive-lined heat shrink tubing, black – 3M EPS-300- 3/4-48

• Where to buy: Waytek Wire
• Quantity: one 48″ stick

3/4″ adhesive-lined heat shrink tubing, red – 3M EPS-300-3/4-RED-48

• Where to buy: Waytek Wire
• Quantity: one 48″ stick

3/4″ heat shrink tubing, clear – DSG Canusa CPX 100 0750 CLEAR

• Where to buy: Waytek Wire
• Quantity: one 48″ stick (minimum purchase will apply)

Standard Large Mounting Plate with kick-out by Yotamac

• Where to buy: Yotamac at Tacoma World
• Quantity: 1

12-10 AWG, #8 hole heat-shrink ring terminals

• Where to buy: Waytek Wire, Del City, or Amazon
• Quantity: 10

12-10 AWG, 1/4″ hole heat-shrink ring terminals

• Where to buy: Waytek Wire, Del City, or Amazon
• Quantity: 1

12-10 AWG, 5/16″ hole heat-shrink ring terminals

• Where to buy: Waytek Wire, Del City, or Amazon
• Quantity: 1

22-18 AWG, 1/4″ hole heat-shrink ring terminals

• Where to buy: Waytek Wire, Del City, or Amazon
• Quantity: 1

Copper Crimp Lug, 4 AWG with 1/4″ hole

• Where to buy: Remy Battery
• Quantity: 1 (possibly more with your setup)

Copper Crimp Lug, 4 AWG with 5/16″ hole

• Where to buy: Remy Battery
• Quantity: 4 (possibly more with your setup)

Copper Crimp Lug, 4 AWG with 3/8″ hole

• Where to buy: Remy Battery
• Quantity: 0 (possibly more with your setup)

Copper Crimp Lug, 4 AWG with 1/2″ hole

• Where to buy: Remy Battery
• Quantity: 0 (possibly more with your setup)

Blue Sea ANL Fuse Holder with Insulating Cover 30- 300A, (Part # 5005)

• Where to buy: Waytek Wire or Amazon
• Quantity: 1

ANL Fuse, 80A

• Where to buy: Waytek Wire or Amazon
• Quantity: 1

22-18 AWG Female Quick Disconnects

• Where to buy: Waytek Wire
• Quantity: 30

22-18 AWG male Quick Disconnects

• Where to buy: Waytek Wire
• Quantity: 2

Fuse Tap

• Where to buy: Amazon
• Quantity: 1

T-Tap Wire Splice, 22-18 AWG

• Where to buy: Waytek Wire
• Quantity: 2

Switch Holder, Six Position V-Series

• Where to buy: OTRATTW
• Quantity: 1

Switches – Carling Technologies Contura V

• Where to buy: OTRATTW
• Quantity: 5

Switch Blank, V-Series Panel Plug

• Where to buy: OTRATTW
• Quantity: 1

Molex Mini-Fit Jr. Male plug connectors, 10-position (Part #39-01-3103)

• Where to buy: Mouser
• Quantity needed: 1

Molex Mini-Fit Jr. Female receptacle connectors, 10-position (Part #39-01-2100)

• Where to buy: Mouser
• Quantity: 1

Molex Mini-Fit Jr. Male pin terminals (Part #39-00-0040)

• Where to buy: Mouser
• Quantity: 9 (minimum purchase will apply)

Molex Mini-Fit Jr. Female socket terminals (Part # 39-00-0038)

• Where to buy: Mouser
• Quantity: 9 (minimum purchase will apply)

In the next part, Part 3 – Tools and Techniques, I’ll show you the tools needed to complete this project as well as the basic technique of crimping terminals.

 

Part 3 - Tools and Techniques



This is part 3 in a series of tutorials teaching you how to build a Bussmann RTMR fuse/relay block. In previous parts, we’ve discussed what the Bussmann RTMR is and why you would want one. I’ve also outlined all of the necessary parts and where they can be purchased. In this part, I’m going to discuss the various tools and techniques needed to complete this project.

TOOLS

There are a few specialty tools that you’re going to need for this project. Let me outline them first. Afterwards, I’ll demonstrate some specific techniques that are required. To start, here’s a list of tools you’ll need to complete this project:

• Wire cutters
• Wire strippers
• Crimpers
• Terminal removal tools
• Soldering iron
• Heat gun

And as a reminder, I take no responsibility for damage, accidents, or injuries resulting from the fabrication or installation of any electrical modifications to your vehicle. You do so at your own risk.

WIRE CUTTERS

Cutting wire is a very basic technique. I should probably not even say anything, but I want to point out that you’ll need two different types of cutters. You’ll need a general purpose wire cutter, also known as a dike, such as the following. This will be used for cutting all of your small wiring used in this project, 18-10 AWG.


You’re going to also need a large gauge wire cutter to cut the main power and ground wiring, which will be 4 gauge. I use a QuickCable 9″ QuickCutter 1 Cable Cutter, Part #4275, that you can buy from Century Tool & Equipment. This particular cutter can cut up to 2/0 AWG wire.


Of course, these specific tools are not required. As long as you have something that will sufficiently cut your wire, you’re good to go.

WIRE STRIPPERS

Stripping wire is not very difficult either. However, there are definitely good wire strippers and poor ones. I’ve been through my fair share of bad wire strippers over the years, so the cost of a good quality wire stripper is well worth it.

I highly recommend getting a wire stripper that not only cuts the insulation, but also removes it at the same time. It can really speed up the process when cutting many wires. I personally use the Klein Tools Katapult® Wire Stripper/Cutter, Part #11063W, which can strip 22-8 AWG wire.


In addition to one of the above stippers, you’re going to need a way to strip the insulation off of larger gauge wire. You can always use a utility knife, but you run the risk of cutting strands of wire. Therefore, a stripper such as a QuickCable Quickstrip Cable Stripper Tool, Part # 4215, is the perfect tool for the job. This can be purchased at Century Tool & Equipment.


CRIMPERS

This project involves several types of terminals, Metri-Pack, Weather-Pack, heat shrink ring terminals, and lugs. Therefore, a variety of crimpers is needed to complete this job.

Metri-Pack and Weather-Pack T-18 Crimper


In order to crimp Metri-Pack and Weather-Pack terminals, you’ll need a special crimper. The T-18 crimper is a low-cost tool that allows you to crimp 24-14 AWG wire as well as Weather-Pack, Metri-Pack 150 and Metri-Pack 280 cable seals. This tool can be purchased from

Del City Crimp Tool for Weather Pack and Metri-Pack 150 & 280 (1 Per Quantity)

Amazon or Del City.

• Crimps Metri-Pack 150 and 280 terminals as well as Weather-Pack terminals.
  
• Crimps conductor and cable seals in separate cavities, requiring two crimps to complete termination.
• Cable seal crimps are “O” type and are produced in two cavities: #1 – Metri-Pack 150 and #5 – Metri-Pack 280 and Weather-Pack.
• Conductor crimps are “B” type and are produced in three cavities: #4 – 16-14 AWG, #3 – 20-18 AWG and #2 – 24-22 AWG.

Open Barrel T-11 Crimper


In this tutorial, I’ll be using 10 AWG wire. In order to crimp the cable seals for this sized conductor, the T-18 crimper noted above can be used. However, to properly crimp 10 AWG terminals, you’ll need an additional crimper. Any open barrel crimper capable of crimping 10 AWG wire should suffice, but another low-cost tool is the T-11 crimper. The T-11 uses the same crimp cavities as the Delphi/Packard 12085271 tool, but is built with an inexpensive, non-ratcheting frame. This tool has a total of five crimp cavities, three of which are for conductor crimps and the other two for insulation crimps. This tool can be purchased from

$43 Delphi Packard Five-cavity Wide-range Crimping Tool 22-12 AWG / 24-14 AWG

Amazon.

• Crimps a wide variety of open barrel contacts in medium size wire ranges.
  
• Crimps conductor and insulation portion of contacts in separate cavities, requiring two crimps to complete termination.
• Insulation crimps are “B” type and are produced in two cavities: A – 18-14 AWG and B – 24-20 AWG.
• Conductor crimps are “B” type and are produced in three cavities: C – 16-14 AWG, D – 20-18 AWG and E – 24-22 AWG.

Although the T-11 crimper is a tool designed to crimp open barrel terminals with 24-14 AWG wire, we can actually use it to crimp 10 AWG wire. This is possible because we don’t need a tool to do any open barrel insulation crimps. Furthermore, the “B” cavity is the proper shape and size for a 10 AWG conductor crimp. The following table lists which cavity to use for a specific wire gauge.

T-11 Crimper Settings
Wire AWG -- Conductor Crimp Cavity -- Insulation Crimp Cavity

• 24 -- E -- B
• 22 -- E -- B
• 20 -- D -- B
• 18 -- D -- A
• 16 -- C -- A
• 14 -- C -- A
• 12 -- B -- n/a
• 10 -- B -- n/a

Molex Mini-Fit Jr. Crimper

This tutorial outlines installation of switches in the overhead console sunglass holder, so I will not be using switchbacks. Therefore, to allow the switches to be removed for any reason, I needed some sort of connector. I chose Molex Mini-Fit Jr. connectors. As an alternative, you could use male and female quick disconnects if you would like to save some money and not buy another tool.

The Molex Mini-Fit Jr. terminals are extremely small and need a special crimper to accommodate them. This is the inexpensive version and can be purchased at Amazon or Mouser.


Heat Shrink Terminal Crimper

You’re going to need a crimper for heat shrink insulated terminals. A very basic and low-cost crimper is the TEKTON 3775, available from

TEKTON 3775 8-in-1 Electrician's Combination Tool

Amazon.


For more consistent crimps, you can use a ratchet crimper. Although not a requirement, this style crimper ensures a proper crimp, because it requires the tool to be fully closed before the automatic release opens.

If you decide to purchase a ratchet crimper, you need to know that there are several types of ratchet crimp tools. Since we are using heat shrink terminals in this project, you’ll need a Single Crimp ratchet tool versus a Double Crimp ratchet tool.

A good choice is the Ancor 702010 Marine Grade Electrical Single Crimp Ratchet Tool, which can be purchased at

ANCOR MARINE GRADE 702010 Electrical Single Crimp Ratchet Tool

Amazon.


Large Gauge Lug Crimper

To crimp lugs onto larger gauge wire, you’ll need a heavy-duty crimper. There are several options in different price ranges that will allow you to crimp these lugs.

E-Z Red B790C Hammer Indent Crimper Tool available at

$26 EZRED B790C Hammer Indent Crimping Tool, Crimps 8 gauge to 4/0 AWG

Amazon.



Hydraulic Crimper available at

TMS 16 Ton Hydraulic Crimper available at

TMS Crimper-WL-YQK-300 16 Ton Hydraulic Wire Battery Cable Lug Terminal Crimper Crimping Tool 11 Dies

Amazon.



E-Z Red B795 Crimper available at

$139 E-Z Red B795 Heavy Duty Crimping Tool

Amazon.



Finally, there’s the Quick Cable 4255-001 crimper available at Battery Mart, which is what I use.



TERMINAL REMOVAL TOOLS

These are not required tools, but if you make a mistake and need to remove a terminal from the Bussmann RTMR or a connector, you’re going to need a Terminal Removal Tool. Each different type of connector has a specific terminal removal tool.

Metri-Pack Removal Tool

The Metri-Pack Removal Tool is made to specifically remove Metri-Pack terminals from their connectors. This can be purchased at Waytek Wire.


I found that the removal tool works as intended when removing tanged terminals from Metri-Pack connectors. However, when trying to remove terminals from the Bussmann RTMR, it’s actually too small and simply isn’t strong enough. I struggled for a long time using the official removal tool, all the while thinking that I was doing something wrong. After many failed attempts and a few successes, I figured that the tool was the problem and not me. I then grabbed a trusted friend, a small green screwdriver with a 3/32″ flat head, and it’s been easy street ever since. The Xcelite R3322 is perfect and can be purchased at

$16 Xcelite R3322 Chrome Vanadium Steel Slotted Round Blade Pocket Clip Screwdriver, Green Handle, 3/32" Head, 2" Blade Length, 4-1/4" Overall Length

Amazon.


Weather-Pack Removal Tool

A Weather-Pack Removal Tool, Delphi Part #12014012, is needed to remove Weather-Pack terminals from their connectors. This can be purchased at Waytek Wire.


Mini-Fit Jr. Terminal Removal Tool

A Molex Mini-Fit Jr. Terminal Removal Tool, Part #11-03-0044, is needed to remove Mini-Fit Jr. terminals from their connectors. This can be purchased at Mouser.


Switch Actuator Tool

There is a special tool needed to remove Carling switches from the switch panel or to replace the switch rockers. This isn’t a required tool, but it’s so inexpensive that you might as well add this to your shopping cart when making your purchase for switches. This can be purchased at OTRATTW.


SOLDERING IRON

There are many different types of soldering irons available, and I’m not going to get into the specifics. I’m recommending a soldering iron to use after crimping the terminals, because we are hand crimping and not using a machine crimper. This is the soldering iron I use that I’ve had for many years. It allows me to control the temperature of the iron based on my needs. It’s a Weller STATION 50/60W 120V WES51, which can be purchased at

Weller WES51 Analog Soldering Station

Amazon.


HEAT GUN

A heat gun is used to shrink tubing and heat shrink terminals. Again, there are many different types available. The one I’ve used for many years is an Eazypower Heat Gun. This is considered a low-end tool for occasional use, but it’s always done a good job for me. If you’re looking to buy one, I recommend finding one with a heat shield. This will make shrinking tubing easier and quicker.



TECHNIQUES

The actual process of building a Bussmann RTMR is very easy. It’s simply measuring, cutting, and stripping wire. Additionally, it requires crimping terminals onto these wires. With this said, I could probably forgo talking about the process and just move on to the actually building. But I think a brief discussion about how to crimp Metri-Pack and Weather-Pack terminals will be helpful.

For technical information about crimping in general, Cycle Terminal has some useful information. Additionally, Molex offers their Industrial Crimp Quality Handbook and their Quality Crimping Handbook.

The technique of crimping terminals is very easy. I’ll demonstrate with 10 AWG wire and Metri-Pack terminals. The process for Weather-Pack terminals is identical. As mentioned above, I have to use two different crimpers, the T-11 for the conductor and the T-18 for the cable seal. The process for 14 AWG wire and smaller is the same, but the T-18 crimper is all that’s required.

After cutting your wire to length, start by stripping the insulation about 7/32″.


Slide cable seal into place. With small gauge wire, it might be easier to slip on the cable seal before stripping and then slide into place afterwards. Otherwise, you risk bending the conductor strands. With 10 AWG, it doesn’t matter.


Using the T-11 crimper, insert terminal into cavity “B”, aligning the tabs for the conductor, and close the jaws just enough to hold terminal in place.

Then insert wire so the cable seal is properly aligned with crimp tabs and the wire is just past the wire crimps. Complete the conductor crimp by firmly squeezing the crimper closed.


The crimp will look like this when completed. Notice that a short length of wire protrudes past the crimp. This is intended and required for a good crimp.


Then, using the T-18 crimper, insert the terminal into cavity “5″, aligning the tabs for the cable seal. Complete the cable seal crimp by gently squeezing the tool closed. You don’t need to squeeze the crimper as firmly as you do for a conductor crimp. Furthermore, with 10 AWG TXL wire and blue cable seals, you need to be careful not to crimp too firmly. Otherwise, you risk splitting the seal.


It will look like this after crimping the cable seal.


As demonstrated, I needed to use two different tools when terminating 10 AWG wire. However, when using 18 AWG wire, the T-18 is all that’s needed. You would simply use cavity “3″ for the conductor and cavity “5″ for the cable seal.

One last tip, because we are using a hand crimper instead of a machine crimper, it’s recommended to solder the terminals. If you choose to solder, this would be the time to do so.

CONCLUSION

This part has outlined all of the necessary tools you’ll need to build the Bussmann RTMR. It’s also shown you how to crimp Metri-Pack and Weather-Pack terminals. Next, in Part 4 – Wiring and Schematics, I’ll get into the details of the Bussmann RTMR and the wiring connections.

 

Part 4 - Wiring and Schematics



This is part 4 in a series of tutorials teaching you how to build a Bussmann RTMR fuse/relay block. In previous parts, we’ve discussed what the Bussmann RTMR is and why you would want one. I’ve also outlined all of the necessary parts, tools, and techniques needed to complete this project. In this part, I’m going to talk in more detail about the RTMR, relays, wiring, and schematics.

Let me begin by saying that this tutorial is not written to teach you the basics of electricity. There are far better tutorials and sources of information for you to learn from. Furthermore, entire books have been written about the subject, so I wouldn’t even be able to do it justice.

Instead, I’m going to talk very specifically about what you need to know in order to wire the Bussmann RTMR enclosure and accessories.

• How a Relay Works
  
• Bussman RTMR Details
• Connections
• Accessory Grounds
• Wire Gauge
• Connectors

And as a reminder, I take no responsibility for damage, accidents, or injuries resulting from the fabrication or installation of any electrical modifications to your vehicle. You do so at your own risk.

How a Relay Works

The Bussmann RTMR uses ISO 280 Micro or Mini relays, with 2.8 mm terminals, and can accommodate either 4-pin or 5-pin relays. But what’s the difference? And what exactly is a relay and why do you want to use one?

A relay is an electrical component that is basically a switch. Many relays use an electromagnet to engage the switch, and are used where you would want a low powered circuit to control a high powered circuit. This is done for safety reasons.

For example, in our application, we will have a switch in the vehicle cabin. To be safe, we want this to be low current. When actuated, a low-powered signal energizes the electromagnet in the relay which triggers the internal switch and allows high current to flow to the accessory. So the switch at your fingertips is the low-powered circuit used to control the high-powered circuit of your accessory via the relay.

Automotive relays typically come in either 4-pin or 5-pin versions. These pins, or terminals, have standard designations.

• 30 = constant power from battery positive terminal (direct)
• 85 = coil ground
• 86 = coil power
• 87 = switched power to accessory
• 87a = normally closed contact with power connected from pin 30 (on 5-pin relays)

The Bussmann RTMR can use either version, but I find that 4-pin relays are sufficient for my needs. I simply want a switch in my vehicle to turn an accessory on or off. Therefore, this tutorial focuses on 4-pin relays only.

The relays we’ll be using are Song Chuan 301-1A-C-R1, which can be purchased from Waytek Wire or Mouser. Notice in the following picture how the pins are labeled on the bottom of the relay. You can even see where the fifth pin, 87a, would be if this was a 5-pin relay. Because the pins are in specific positions, it makes a difference how the relay is inserted into the Bussmann RTMR. I’ll talk in more detail about this later.


For now, let me show you a simple wiring diagram that details how to connect a switch and accessory to a relay.


From this diagram, you can see that we have a physical switch, which will be inside our vehicle cabin. This supplies a positive signal to pin 86 of the relay. This pin is the input terminal to the coil inside the relay. This configuration is called "switched-power", because the switch is turning power on and off to the relay. This is a low-current circuit, which is 97.5mA at 12 volts per the datasheet for the relays I’m using.


Contrast this with a typical accessory such as a 100 watt off-road light that uses over 8 amps at 12 volts. That’s 80 times more current and something you don’t want running through a switch at your fingertips.

When current is sent to the coil, it creates a magnetic field that closes the internal switch. With power connected to pin 30 directly from the battery and with the accessory connected to pin 87, the circuit is complete when the switch is closed. High power flows to the accessory directly through the relay and not your switch.

Now that you understand the basics of connecting an accessory to a relay, keep this in mind as I outline the details of the Bussmann RTMR.

Bussmann RTMR Details

As stated in Part 2 – Parts, there are several different configurations of the Bussmann RTMR. For this tutorial, I’m specifically using model 15303-2-2-4, which accommodates five relays and ten fuses. It also has two internal busbars. Let’s look at the details of this particular configuration and how we would wire it. Once you understand this, you could easily adapt what you’ve learned to any of the other RTMR enclosures.

When first looking at the Bussmann RTMR, you might be quickly overwhelmed with the number of holes, or cavities as they’re called. It’s very similar to looking at a mixing console in a recording studio. There’s a whole lot of the same going on, and it can be dizzying at first sight. On a mixing console, you just need to learn one channel strip and you understand the majority of the mixing board. Similarly, all you need to learn on the RTMR is two rows of cavities, and the remaining simply repeat. So let’s break it down.

On the top of the RTMR, you’ll see that the relays are down the left side. For each relay, there are five insertion cavities to accept the male terminals. Down the right side are two insertion cavities for each fuse. You’ll quickly see that a relay takes up two rows of cavities, yet a fuse only takes one. Therefore, for each relay position, there are two fuses. But the physical layout does not imply that the relay and fuses are connected together.


If you look at the cavities in more detail, you’ll notice two different types. One shape, which is the larger of the two, is where the male terminals of the relays and fuses insert. The other is a smaller cavity that is used in conjunction with a Terminal Removal Tool to allow you to remove the female terminals and wiring from the backside. The following picture illustrates the differences.


On the bottom of the RTMR, the relays are oriented on the right and the fuses are on the left. Additionally, there are two internal busbar stud mounts at the bottom.




Considering the fuses, you’ll see that there are two cavities on the top side for the terminals, yet there is only one on the bottom. This is because one leg of each fuse is connected to the internal busbar, and the other leg is available to connect a female terminal and wire to.

With regards to the relays, you’ll observe on the top side five cavities for the male terminals of each relay. On the bottom, there are five as well, but they don’t exactly line up with what’s on top. This is because one terminal inserted into the top is connected to the second internal busbar. Also, there is another cavity on the bottom that isn’t accessible from the top-side with this specific enclosure model. This is because there’s a sticker on the top surface that blocks this hole.

This might all sound confusing at the moment, but study the following picture. It should clear things up.


You’ll notice that pin 86 is not accessible on the bottom. That’s because this pin is connected to the second internal busbar, which will be used to proved power to the relay coils. To complete the circuits, we would wire the device to send power out pin 85 to the switches, which would then continue to ground. Notice that this is contrary to the relay diagrams that I detailed earlier. Instead of switching power to the relay, we are switching ground. However, the circuit works just the same and is simply a different way of utilizing a relay.

With this configuration, we can supply power to the second internal busbar from a spare fuse in the Bussmann, or directly from the battery. The compromise is that power would be available to your accessories at all times, even with the ignition off. If you need these circuits active with your ignition, then an alternate solution is to provide power to the internal busbar using a fuse-tap at the OEM fuse panel from a circuit that is only on when your ignition is on.

I have a problem with this setup. Basically, I do not like terminating ground at some location on the frame or body. Therefore, to return ground from the switches back to the busbars at the RTMR while also supplying power from the OEM fuse panel, it would require an additional wire traveling through the firewall for a total of seven. This isn't that big of a deal until you discover that Weather-Pack connectors are limited to six circuits. Therefore, since I've chosen to use a six-position Weather-Pack connector, I'm limited to six wires, and I need to come up with an alternate solution. This might seem unconventional, but if we install the relays upside-down as shown below, then our problem would be solved.


With this setup, power is supplied to your switch inside your vehicle and connects to pin 86 when the switch is engaged. This circuit will connect to your in-dash fuse block with a fuse tap, which protects this wire. Next, pin 85, which needs to be connected to ground, is connected to the internal busbar. Therefore, we will use the second internal busbar for grounding pin 85 on all relays. This is a much cleaner setup and makes better use of the RTMR.

As a side note, if you chose to use a 5-pin relay, then pin 87a would be in the top-center position, but this is currently covered up with the overlaying sticker. In order to insert the terminal, you simply need to cut out part of the sticker that covers the cavity.

Connections

Now that we know how to wire an accessory to a relay and we know we’re going to install the relays upside down, we can use the following diagram to illustrate how to connect them to the Bussmann RTMR.


Notice that we only use one fuse, which supplies power to pin 30 through a short length of wire. This will be a high current signal, which continues through the relay’s internal switch and out pin 87 to the accessory.

The accessory is connected to pin 87 with a custom length of wire depending on the its location.

Your switch is connected to pin 86 and with a wire routed through your vehicles firewall.

Pin 85 is the switch ground and is connected to the second internal busbar.

The two additional middle cavities for the relay are not used.

Therefore, you only need three wires per relay connected directly to the Bussman RTMR to connect an accessory. I’ll show you how to make all of these wires with crimped terminals in the next part, Part 5 – Building the RTMR.

Accessory Grounds

There is another wiring issue to consider, though, and that is with regards to your accessory grounds. You have options here, but some are better than others.

One popular technique, although not highly recommended, is to connect the accessory ground at a nearby location, such as the vehicle frame or body. This isn’t recommended due to the ground point being inconsistent or of lower conductivity.

A second option is to connect all accessory grounds directly to the battery. Although this might provide a perfect ground, the side effect is messy wiring, and it somewhat defeats the purpose of installing a fuse/relay block.

A third option is to group all of the accessory grounds together. I’ve seen other installations where the ground wires are simply bundled or spliced together. Although this may work if the wire gauge is rated to handle the combined load, I feel it looks unprofessional and has the potential to be unsafe.

The final and preferred option, is to use busbars external to the Bussmann RTMR to attach your grounds to. I find this safer, more reliable, and a cleaner way to route your accessory grounds. I’ll detail the specifics with regards to installation and connection in Part 5 – Building the RTMR.

Wire Gauge

Now that you know how to connect everything together, you just need to know what size wire to use. Simply put, you use a wire gauge rated to handle the current of your accessory. Unfortunately, when trying to find the answers to this question, you’ll quickly see that there are many conflicting charts. This is because there is no single definitive chart for our application, and because there are many factors that go into ampacity rating. Wire length, ambient temperature, insulation type, and free air space are all contributing factors in addition to the cross-sectional area of a wire.

So with that said, this is a conservative chart that will accommodate our needs.

• 18 gauge – 7 amps
• 16 gauge – 10 amps
• 14 gauge – 15 amps
• 12 gauge – 20 amps
• 10 gauge – 30 Amps

Notice how I am not listing any wire size smaller than 18 gauge. This is intentional. I don’t want to use wire smaller than 18 gauge, because it can be a bit difficult to work with while using the Bussmann RTMR.

When wiring the RTMR, there are two circuit types: accessories and relay coils. The current requirements for the relay coils are many times less than the accessories. Furthermore, the coils are a known and constant rating, no matter what type of accessory is installed. As stated earlier and outlined in the datasheet, the current needed to energize the relay coil is 97.5mA at 12 volts. I also stated that I don’t want to use any wire smaller than 18 gauge. Therefore, I’ll be using 18 gauge wire to connect the switches to pin 86 of each relay. This is more than sufficient to handle the relay coil load.

With regards to connecting accessories, there are two different approaches to wire size selection when wiring the RTMR. One approach is to plan everything out in advance, with all of our accessories and current demands known beforehand. This would allow us to build the RMTR with the exact size wire we need for that specific accessory. You then build the enclosure and connect your accessories to the specific circuit where you want your switch. Great! But this doesn’t allow you to modify, adapt, or upgrade anything easily in the future. Therefore, the second approach is to build the RTMR so that each circuit can handle the maximum load that you may need, regardless of how many high-powered accessories you plan to install. Let me explain.

If I wire three of the circuits with 14 gauge wire and only two with 10 gauge, then I’m restricted to two circuits that can accommodate high-powered accessories. Furthermore, I’m also restrained on where the switches for these specific accessories are in my vehicle. This is the nature of the beast. Let’s say the first two relays are wired with 10 gauge. That means only the first two switches connected to these relays can be used for these accessories. But what if I wanted to reorganize my switches? What if I wanted to upgrade or swap out for a higher-powered accessory? This is where the other wiring approach comes in.

If I wire all five circuits of the RTMR with 10 gauge wire, then I have much more flexibility. I’m not limited to the number of accessories (within the five), and I’m not restricted to which circuit that accessory can be on. This means that I can choose any switch in my vehicle at any time. To swap accessories around, simply connect the accessory to a different circuit and change switch rockers. The wiring and switch bodies all stay in place. I know it can handle the load, because I’ve wired up the RTMR from the beginning to do so.

Now there’s a big warning here. The Bussmann RTMR is rated to a maximum of 80 amps. This is for each internal bus. The first internal bus is providing power to all ten fuses, and the second internal bus is providing ground for the switches. With five switches only needing 97.5mA each to energize the relay coil, this bus will never go over 1/2 amp, so it’s not of concern. However, we cannot go over 80 amps for the first internal busbar, which supplies power to all ten fuses.

So keep in mind that for all accessories, whether they’re connected through the relays or directly to a fuse, you cannot go over 80 amps. This does not mean you cannot connect accessories that total more than 80 amps when combined. It just means that you cannot use them all at the same time when their combined total will go over 80 amps. There is a clear distinction here. Therefore, your choice is to be very careful when using multiple accessories at the same time or to total their power requirements when purchasing so that they don’t go over 80 amps.

This might sound confusing, but you just have to do a bit of math and thinking beforehand. In a real-world application, you most likely won’t be hitting this 80 amp ceiling, but you’ve been warned.

Connectors

To allow for maximum flexibility, I’ll be installing Metri-Pack 280 Series connectors for the accessory wiring. This is what will make installing or swapping accessories very easy. Without this connector, your hands are still tied, even though we’re using 10 gauge wire. The accessory wiring would be a direct connection to the RTMR, so modifications would require the enclosure to be removed from the vehicle. This isn’t very flexible.

I’m choosing to use Metri-Pack 280 Series connectors instead of Weather-Pack connectors, because they have a higher current rating. Whereas Weather-Pack connectors are rated at 20 amps, Metri-Pack 280 Series connectors are rated at 30 amps. Therefore, they are a perfect match when using 10 gauge wire.

When installing the Metri-Pack connectors, I’ll run a positive wire from pin 87 to the connector and a ground wire from the external ground busbar to the connector. Both of these will be 10 gauge wire. This connector is your direct attachment point for an accessory. Look at the following diagram where I’ve updated it to show the external ground busbar, wire sizing, and connector.


Now the cool thing is that when installing an accessory to the Metri-Pack connector, you’re not required to use 10 gauge wire between the accessory and the connector. Instead, you use the appropriate sized wire to connect your accessory to the Metri-Pack connector based on the need of that accessory. Then install a fuse in the RTMR for this circuit to match the wire size. Use the same chart I listed earlier when selecting fuse size.

• 18 gauge – 7 amps
• 16 gauge – 10 amps
• 14 gauge – 15 amps
• 12 gauge – 20 amps
• 10 gauge – 30 Amps

For example, if using 14 gauge wire for an accessory, install a 15 amp fuse. It doesn’t matter that the jumper wire from the fuse to pin 30 is 10 gauge or that the wires between the Metri-Pack connector and RTMR are 10 gauge. These have a higher ampacity rating, so you’re safe. The rule is that a fuse protects the wire. In this example, it needs to protect the smallest gauge wire in the circuit, which is 14 gauge.

With this new information, I’ve updated our wiring diagram once again to include the accessory. I’ve also indicated that the wire size from the Metri-Pack connector to the accessory has not been specified. You will make this choice based on your needs.


On a side note, I want to point out that fuse selection is important for not only the wire rating, but also the connector rating. I mentioned earlier my decision to use Metri-Pack connectors instead of Weather-Pack. If you were to use Weather-Pack connectors, then the highest rated fuse you could use is 20 amps, even if you used 10 gauge wire all the way out to your accessory. The connector has the lowest rating, so it trumps all other wiring.

Anyway, the flexibility of this design lies in the combined use of Metri-Pack connectors and 10 gauge wire for all direct accessory connections to the RTMR. It allows you to use any circuit for any accessory at any time. From this point, you can save a little money when installing wiring from the RTMR out to your accessory by using the correctly rated wire for that specific accessory.

One last note before concluding. I’ll be using is a six-way Weather-Pack connector for the switch wiring traveling through the firewall into your vehicle cabin. I’m using a Weather-Pack connector because a six-way Metri-Pack connector is not available, and it more than sufficiently meets our current needs. Anyway, the reason I used a connector for the switch wiring is for easy installation and any future troubleshooting. Once installed, you won’t be disengaging this connector, but if you ever need to remove the RTMR enclosure, you want to be able to do so easily without cutting any wires.

Conclusion

The following list summarizes what we’ve learned in this part.

• I’ve explained how a relay works, that it’s a device that uses a low-powered circuit to control a high-powered circuit.
• I’ve detailed the specifics of the Bussmann RTMR enclosure. You know which relay terminals the cavities align to.
• The relays will be installed in an upside-down position. This allows you to use the secondary internal busbar as a ground point for pin 85 of the relays.
• I’ve shown you a wiring schematic that details how to connect accessories and switches to the RTMR.
• We’ll be using external busbars in conjunction with the Bussmann RTMR to use as grounding points for all accessories.
• We’ll be using 18 gauge wire for the switches to pin 86.
• We’ll be using Metri-Pack 280 Series connectors rated at 30 amps with accessory wiring. This will allow future flexibility with swapping or upgrading accessories to different circuits.
• We’ll be using 10 gauge wire for the jumper wires from the fuse to pin 30.
• We’ll be using 10 gauge wire for the wiring from the RTMR and external ground busbars to our Metri-Pack connectors. This will allow for maximum current rating on all circuits and maintain a flexible design.
• Fuse selection is made based on protecting the wire. The fuse needs to be chosen to protect the smallest gauge wire for each circuit.
• We’ll be using a six-way Weather-Pack connector for the switch wiring running through the firewall and into the vehicle cabin.

In Part 5 – Building the RTMR, I’ll will walk you through building the RMTR in detail, step by step.

 

Part 5 - Building the RTMR



This is Part 5 in an on-going series of tutorials that will teach you how to build a Bussmann RTMR fuse/relay block for your vehicle. We’ve already covered what the Bussmann RTMR fuse/relay block is, what parts are required, what tools are necessary, and techniques to build it. In this part, we’re going to put it all together so that you will have a completed Bussmann RTMR fuse/relay block that you can install in your vehicle.

There are several steps involved in putting this enclosure together.

• Mounting RTMR and ground busbars to bracket
• Insert cavity plugs into unused cavities
• Making the switch harness
• Making jumper cables
• Making accessory cables
• Installing fuses and relays

And as a reminder, I take no responsibility for damage, accidents, or injuries resulting from the fabrication or installation of any electrical modifications to your vehicle. You do so at your own risk.

MOUNTING RTMR AND BUSBARS

This section will simply mount the RTMR and busbars to the bracket.

Parts used in this section:

Bracket: Standard Large Mounting Plate with kick-out by Yotamac

• Quantity: 1

Busbars: Blue Sea Systems 5 Gang Common 100A Mini Busbars, part #2304

• Quantity: 2

Screws: 10-32

• Quantity: 4

Screws: 10-24

• Quantity: 4

Nuts: 10-24

• Quantity: 4

Let’s begin by installing the RTMR enclosure to the bracket. This is simply done by screwing it into place. The RTMR is inserted from the bottom of the bracket with four 10-32 screws affixing it in place.




Next, we want to mount the two ground busbars. One busbar will be used as the ground bus for the five accessories connected through the relays while the other will be used as the ground bus for the five accessories connected solely through the fuses. I’m using Blue Sea Common 100A Mini busbars. This is a good size, because it’s current rating is slightly higher than the internal busses of the RTMR. Each bus within the RTMR is rated at 80 amps. Additionally, it has five #8-32 screw terminals along with two #10-32 studs. This is a perfect number of attachments for the accessory grounds as well as the primary ground wire to the battery. Last, the physical size and spacing just happens to work out perfectly as you’ll see.

To mount the busbars, I aligned them up on either side of the RTMR, marked the hole locations, drilled holes, and attached with 10-24 screws and nuts. As you can see in the picture, I mounted the busbars with the hardware backwards. Typically, the screw head would be on the side of the busbar with the nut on the backside of the mounting surface. However, to maintain a clean look with only screw heads showing on the top surface of the bracket, I installed the nut into the recessed hole in the busbar instead of the screw. With this particular screw and nut size, the nut wedges into place and prevents it from spinning while tightening. If you use a different screw and nut size or want more reinforcement, you could always add a bit of epoxy on the nuts.







INSERTING CAVITY PLUGS

There are a few cavities in the RTMR that won’t be used, which we need to seal from water and contaminants.

Parts used in this section:

Cavity plugs: Metri-Pack 280 Cavity Plugs – 12010300

• Quantity: 10

If you remember from Part 4 – Wiring and Schematics, we’re using 4-pin relays. As a result, all of the cavities associated with pin 87A on a 5-pin relay need to be sealed with cavity plugs. When looking at the RTMR from the back, this is the entire middle row of cavities on the right side. Simply insert a Metri-Pack 280 green cavity plug into each of these holes.




MAKING SWITCH HARNESS – PART 1

The switch wiring harness is composed of two parts. The shorter part is permanently connected to the RTMR with a Weatherpack connector on the end. The second part has the mating connector and is the longer harness that travels through the firewall to your switches.

Let’s begin by making the shorter switch wiring harness that connects to the RTMR. We need to make this now, because these wires will be inserted into the RTMR before any subsequent wiring, which are installed over the top. They are also 18 AWG wire and can be a bit temperamental when installing. So it just happens to be easier to insert them without any other wires in the way.


The switch harness is composed of six wires. Five circuits are the positive signals from the switches and the sixth is a ground wire for the switch independent LEDs. With six wires in total that need to be passed through the vehicle’s firewall, you have the option of hard-wiring or using a connector. I prefer using a connector so that I can easily remove the entire bracket and RTMR in the future for any reason. Therefore, a Weather-Pack six-way connector is a perfect solution. It’s waterproof, chemical resistant, and the exact size needed.

With multiple circuits, it makes sense to vary the color of each wire. Therefore, I’ll use a different color, excluding red or black, for each of the five circuits. I’ll then add a black ground wire for the switch independent LEDs. The color sequence of the circuits can be in any order that you choose, but I’ve always found that it makes logical sense to alphabetize the colors corresponding to numerical ordering of circuits. This helps me to troubleshoot in the future. Therefore, I’ll be using this specific ordering of wires: black, blue, green, orange, white, yellow.

Now let’s get down to business and make something. The parts I’m specifically using in this step are the following:

Connector: Weather-Pack Six-Way Female – 12015799

• Quantity: 1

Terminals for connector: Weather-Pack Female 20-18 AWG – 12089188

• Quantity: 6

Terminals for RTMR: Metri-Pack 280 Sealed Tangless Female 18-16 AWG – 12110847

• Quantity: 5

Cable seals: Metri-Pack 280, Green 20-18 AWG – 12015323 / 15324982

• Quantity: 11

Wire: 18 AWG GXL

• Colors: black, blue, green, orange, white, yellow
• Quantity: 13″ each color

Ring Terminals: 20-18 AWG heat shrink, 1/4″ hole

• Quantity: 1

Wire loom: 1/4″ expandable braided sleeving

• Quantity: 5″

Heat shrink: 1/2″ adhesive-lined

• Quantity: 3″

Start by cutting one black and five different colored 18 AWG GXL wire, 13″ long.


Set the black wire aside and slip on green cable seals to the colored wires. These need to be installed first, because doing so after stripping can be a bit difficult without bending the exposed wire.


Strip one end of each wire 7/32″ and slide cable seals up into place.


Using the T-18 crimper, crimp Metri-Pack 280 Sealed Tangless Female 18-16 AWG terminals using setting “3”. Then crimp the cable seal using setting “5”.


If you choose to solder your terminals, do so now.


Insert terminals into the Bussmann RTMR to pin 86 for each relay.


These will only insert in one direction. So don’t force the terminal in. If it doesn’t easily insert, then turn it around. I maintained alphabetical ordering of color corresponding to relays one through five.


Strip the black wire 1/4″ long, slip on 22-18 AWG heat shrink terminal with 1/4″ hole, and crimp. Use a heat gun to seal.


Attach black wire to stud on RTMR for the 2nd internal ground bus. Place the wire as follows.


Cut 1/4″ braided sleeving 5″ long and two pieces of 1/2″ diameter heat shrink 1.5″ long. I’m using adhesive-lined heat shrink to help hold everything in place. But this isn’t a requirement, because it’s not sealing any connections.


Gather all of the wires towards the top end of the Bussmann RTMR so that they lay flat and grouped together. Slip on braided sleeving and one piece of heat shrink tubing. Align braided sleeving and heat shrink so that they’re up close to the RTMR with the end of the sleeving in the middle of the tubing. Use heat gun to shrink and hold in place.


Cut wires evenly so that they’re 2.5″ away from the end of the sleeving. Slip on second piece of heat shrink tubing, and slide down the harness a bit. Don’t put into place and use a heat gun yet. We want to install the Weather-Pack connector first and then slide the tubing into place afterwards.


Slip on green cable seals to each wire, strip each wire 7/32″, and slide cable seals into place.


Using the T-18 crimper, crimp Weather-Pack Female 20-18 AWG terminals using setting “3”. Crimp cable seals using setting “5”. If you’re soldering terminals, do so now.


Insert each terminal into Weather-Pack female connector while maintaining correct order of wire colors: black, blue, green, orange, white, yellow. The Weather-Pack connector has labels A-F for each circuit. I started my sequence with “A” as circuit one.





Flip down Terminal Position Assurance latch. This assures that the positioning of the terminals remains within tolerance and will allow the mating connector to align without any problems. Then slide the heat shrink up into place, and use a heat gun to shrink.


MAKING SWITCH HARNESS – PART 2

The second part of the switch wiring harness plugs into the short harness extending from the RTMR, travels through the firewall, and continues to your switches. Additionally, it contains wires for powering the switches and controlling the switches’ independent LED brightness.


The parts I’m specifically using in this section are as follows:

Wire: 18 AWG GXL

• Colors: black, blue, green, orange, white, yellow, red, red/black, brown
• Quantity: 90″ each color

Heat shrink: 3/8″ adhesive-lined

• Quantity: 4″

Heat shrink: 1/2″ adhesive-lined

• Quantity: 2″

Heat shrink: 3/4″ adhesive-lined

• Quantity: 2″

Wire loom: 1/4″ expandable braided sleeving

• Quantity: 151″

Terminals: Weather-Pack Male 20-18 AWG – 12089040

• Quantity: 6

Connector: Weather-Pack Six-Way Male – 12010975

• Quantity: 1

Cable seals: Metri-Pack 280, Green 20-18 AWG – 12015323 / 15324982

• Quantity: 6

This harness contains a total of nine wires:

• Five for the switches
  
• one for the switches’ ground
• one for switches’ power
• one for switches’ independent LED power
• one for switches’ independent LED ground.

Start by cutting one black and five different colored 18 AWG GXL wire, 90″ long. I used the same colors as before: blue, green, orange, white, and yellow.


Slip on green cable seals to each wire, strip each wire 7/32″, and slide cable seals into place. Using the T-18 crimper, crimp Weather-Pack Male 20-18 AWG terminals using setting “3”, and crimp cable seals using setting “5”. If you’re soldering terminals, do so now.


Insert each terminal into Weather-Pack male connector while maintaining correct order of wire colors: black, blue, green, orange, white, yellow. The Weather-Pack connector has labels A-F for each circuit. I started my sequence with “A” as circuit one.


Flip down Terminal Position Assurance latch. This assures that the positioning of the terminals remains within tolerance and will allow the mating connector to align without any problems.


Cut three pieces of 1/4″ braided sleeving 22″ long.


Set two aside and slide one piece over all wires up to the connector. Cut a 2″ piece of 1/2″ heat shrink tubing and slip over sleeving. Slide into place up near connector while positioning the braided sleeving roughly in the middle of the tubing. Use heat gun to shrink in place.


Cut three more wires at 90″ long. One is for all switches’ power, so I used red. Another is for all switches’ independent LED power, so I used red with a black stripe. And the third is for all switches’ independent LED ground, so I used brown.


Using one of the remaining two pieces of 22″ long 1/4″ sleeving, slide over the red wire. Position so that it’s about 2″ from the end. Cut a 2″ piece of 3/8″ heat shrink tubing, slide over the wire and sleeving. Position so that sleeving is roughly in the middle of the tubing and that 1″ of wire is hanging out. Use a heat gun to shrink in place.


Using the last piece of sleeving, slide over the red/black and brown wires. Position so that it’s about 2″ from the end. Cut a 2″ piece of 3/8″ heat shrink tubing, slide over the wires and sleeving. Position so that sleeving is roughly in the middle of the tubing and that 1″ of wire is hanging out. Use a heat gun to shrink in place.


Bundle the three separate wiring harnesses together so that the loose ends are aligned. This will position the wires as shown below. What’s important is that the ends of the braided sleeving in the middle of the wiring are aligned.


Cut an 85″ length of 1/4″ braided sleeving.


Grabbing all nine wires with the ends aligned, slide the braided sleeving over the group, continue until it meets the three shorter sections of braided sleeving.


Cut a 2″ piece of 3/4″ tubing. Slide down the wiring harness and position over the the point in the middle where the various sections of braided sleeving meet. Use a heat gun to shrink in place.


Cut a 2″ piece of 3/4″ heat shrink tubing. Slide over the loose end of all nine wires and position so that the braided sleeving is roughly in the middle. About 2″ of wiring should remain exposed. Trim wiring if necessary. This is what it should look like now.


At this point, you can set the switch wiring harness aside. I’ll continue later with more details about how and where to connect the specific wires during Part 6 – Installation. At this point, however, be aware that you don’t want to install any connectors yet to the wire ends. You’ll want to run it through the firewall first and snake it into place.

MAKING JUMPER WIRES

We need to make five jumper wires that connect power from a fuse to pin 30 of the relay. With five relays, we’ll use five fuses. The other five fuses can be used for non-relay, low-power accessories. Now it’s up to you which fuses you want to use in conjunction with the relays. For example, you can use fuses 1-5, 6-10, odd-numbered fuses, even-numbered fuses, or any crazy sequence that you like. Personally, I used odd-numbered fuses with the relays. I chose to do it this way, because the relays take up two rows of cavities in the RTMR, and the odd-numbered fuses align with the first row of each relay. This makes the wiring layout clean and elegant. Ultimately, it doesn’t make a difference.

The parts I’m specifically using in this step are the following:

Terminals for RTMR: Metri-Pack 280 Sealed Tangless Female 12-10 AWG – 12110853

• Quantity: 10

Cable seals: Metri-Pack 280, Blue 12 AWG – 12015193 / 15324981

• Quantity: 10

Wire: 10 AWG TXL

• Colors: red
• Quantity: 17.5″

Cut five lengths of 10 AWG red wire 3 1/2″ long.


Slip on blue cable seals to both ends, strip each end 7/32″, and slide seals up into place.


Using the T-11 crimper, crimp Metri-Pack 280 Sealed Tangless Female 12-10 AWG terminals with setting “B” on both ends while making sure that they face the same direction. Using the T-18 crimper, crimp the cable seals with setting “5”. If soldering terminals, do so now.


The next step is to insert the jumper wires. Start by bending the wire into a horseshoe shape, making sure that the terminals are facing the same direction.


Then insert one end into an odd-numbered fuse cavity. Finally, insert the other end of each wire to pin 30 of it’s corresponding relay.


Continue with the remaining wires and it will look like the following when complete.


MAKING ACCESSORY CABLES

This section will outline the steps necessary to build the following cable assembly.


This cable and connector is what you use in the future to attach any accessories to your vehicle, such as lights and compressors. In total, you will need to make ten of these cable assemblies. Five will be for accessories through relays, and the other five will be for fused only, low-power, accessories.

The parts I’m specifically using in this step are the following:

Connector: Metri-Pack 280 Two-Way Female – 15300027

• Quantity: 10

Terminal Position Assurance (TPA) clip: Metri-Pack 280 Terminal Position Assurance clip – 15300014

• Quantity: 10

Terminals for connector: Metri-Pack 280 Sealed Tanged Female 12-10 AWG – 12077413

• Quantity: 20

Terminals for RTMR: Metri-Pack 280 Sealed Tangless Female 12-10 AWG – 12110853

• Quantity: 10

Cable seals: Metri-Pack 280, Blue 12 AWG – 12015193 / 15324981

• Quantity: 30

Wire: 10 AWG TXL

• Colors: red, black
• Quantity: 55″ red, 75″ black

Ring terminals: 12-10 AWG heat shrink, #8 hole

• Quantity: 10

Heat shrink: 1/2″ adhesive-lined black

• Quantity: 35″

Heat shrink: 3/4″ clear

• Quantity: 10″

Please note that you will be using two different styles of Metri-Pack terminals. The Metri-Pack plugs use a “tanged” terminal, and the Bussmann RTMR uses “tangless” terminals.

Another detail to consider is that we are using two ground busbars, one on either side of the RTMR. I mention this because it makes a difference in how the cable assemblies are made. The five cables for the accessories through the relay are made slightly differently than the five cables for the fused-only accessories. The only difference is that they are mirror images of each other, which flips the terminal alignment. You’ll see what I’m talking about as we proceed.

This step is a bit more involved than anything we’ve done before. So let’s start by making a single cable assembly that can be used for a relay accessory. When complete, simply make four more identical cables. When done with these five, I’ll outline the differences for the remaining five cables.

Cut one 10 AWG red wire to length, 5 1/2″, and cut one 10 AWG black wire longer than needed, approximately 7 1/2″. Strip one end of each wire 7/32″ and slip on blue seals.


Using T-18 crimper, crimp Metri-Pack 280 Sealed Tanged Female 12-10 AWG terminals to each using setting “B”. Using T-18 crimper, crimp cable seal with setting “5”.


If you’re choosing to solder the terminals, do so now.


Insert into Metri-Pack plug with the red wire into the “A” hole and the black wire into the “B” hole. This isn’t a requirement, but you want to at least maintain consistency for all your cable assemblies. If you swap the order, all it does is orient the plug in the opposite direction.


Snap on blue Terminal Position Assurance clip. There is no specification as to which side the clip is attached to. I chose this orientation and maintained consistency for all cables.


Cut 1/2″ diameter heat shrink tubing 3 1/2″ long.


Slip on heat shrink all the way to the retainer clip and use a heat gun to shrink the tubing.


Print a label using a label maker to indicate which accessory this is. For this example, I’m inserting into the first relay, which is using the first fuse. Therefore, I labeled as “F1R1” to indicate Fuse #1 and Relay #1. I mentioned earlier that I’m using odd-numbered fuses, so the next cable would be labeled as “F3R2”. Last, use a 1″ long piece of 3/4″ clear heat shrink tubing to keep in place.


Slip on blue cable seal, strip the exposed end of red wire 7/32″, and slide seal into place:


Align Metri-Pack 280 Sealed Tangless Female 12-10 AWG terminal as shown in the following image. Notice how with the cable laying flat on a table, the red wire is towards the top and the opening of the terminal crimps is towards you. This will ensure that the black wire is on the side near the Blue Sea busbar when the red wire is inserted into fuse block.


Crimp terminal with “B” setting, and crimp seal with “5” setting. If you choose to solder terminals, do so now.


Attach sealed 12-10 AWG heat-shrink ring terminal with #8 hole to correct position on busbar. For this example, the cable assembly will be inserted into the top relay, so I’m using the top busbar position. As each subsequent cable is inserted, I’ll use the next busbar position.


Bend the black wire to the side, push the switch harness wires towards the center, and temporarily slip the red wire into the fuse block to pin 87.


Do not seat all the way. We are simply putting the cable in place to align the black wire up against the ring terminal to determine what length to cut it at.


Align the black wire to the ring terminal, mark, and cut to length.


Remove cable assembly and ring terminal. Strip black wire 1/4″.


Lay the cable on a flat surface with the black wire bent out to the side as shown below. Slide on the ring terminal, and orient it so that the blade is angled 90° from the surface and facing towards the connector. This will ensure that the terminal it will lay flat once installed in the fuse block.


Crimp ring terminal, use heat gun to seal, and install permanently into fuse block. You’ll know the red wire is fully seated when it clicks into place.


Once installed, it will look like this.


After that, make four more cables with the same technique, and it’ll look this this.


Now we need to make five more cables for the fused-only accessories. The overall process is exactly the same, but there is a subtle difference in the cable assembly process.

Simply put, we need to position the terminal differently on the red wire that inserts into the RTMR. All you need to do is flip it 180°, as the following image illustrates. This is opposite of how you did it before. Whereas the red wire was on top with the cable laying flat on a table, the red wire is now on the bottom, and you position the terminal crimps facing towards you as before. When the red wire is inserted into the RTMR, the black ground wire will stick out to the other side towards the second busbar.


As an additional observation, when you slip on the ring terminal to the black wire for the ground busbar, it will look like the following. It’s still facing up towards the Metri-Pack connector, but the image shows that the terminal is facing the opposite direction.


These five cables are not using any relays. Instead, they are inserted into the even-numberd fuse positions. So the first cable will be in fuse #2, the second in fuse #4, an so forth. After making and installing the five fused-only accessory cables, it will look like the following image.


Completing The Build

The final step is making and connecting the power and ground cables as well as inserting relays.

Parts used in this section:

Fuse holder: Blue Sea ANL Fuse Holder with Insulating Cover 30- 300A, Part #5005

• Quantity: 1

Fuse: 80A ANL

• Quantity: 1

Wire: 4 AWG welding wire

• Colors: red, black
• Quantity: About 2-4′ each color.

Copper Crimp Lug: 4 AWG with 1/4″ hole

• Quantity: 2 (possibly more with your setup)

Copper Crimp Lug: 4 AWG with 5/16″ hole

• Quantity: 2 (possibly more with your setup)

Copper Crimp Lug: 4 AWG with 3/8″ hole

• Quantity: 0 (possibly more with your setup)

Copper Crimp Lug: 4 AWG with 1/2″ hole

• Quantity: 0 (possibly more with your setup)

Wire loom: 1/2″ expandable braided sleeving

• Quantity: About 2-6′

Wire: 10 AWG TXL

• Colors: black
• Quantity: 3″

Ring terminals: 12-10 AWG heat shrink with 1/4″ hole

• Quantity: 1

Ring terminals: 12-10 AWG heat shrink with 5/16″ hole

• Quantity: 1

Heat shrink: 3/4″ adhesive lined

• Colors: red, black
• Quantity: about 6″ of each color

Relays: Song Chuan 301-1A-C-R1 four-pin

• Quantity: 5

Let’s begin by installing the relays. As mentioned previously, we are installing these upside down. So start with one relay as shown below, and then continue until all five are inserted.


I won’t be installing the individual fuses now. I do that whenever I install an accessory to the vehicle. This is because I don’t know what sized fuse I’m going to need until the accessory and wire size are chosen.

Next, we need an overall circuit protection device for the RTMR. I used an ANL fuse holder, but you could use a circuit breaker if you prefer. This was installed on the top-side of the bracket.


Now let’s make a supply wire to provide power from the ANL fuse holder to the RTMR.


I made mine just long enough to connect the two together without any slack. And as before, I used 1/2″ braided sleeving and 3/4″ adhesive-lined heat shrink tubing. The crimp lugs used were 4 AWG with 5/16″ hole. I found that it’s easiest to cut the cable in place as follows:

• cut wire longer than needed
• strip one end
• crimp lug
• install to fuse holder
• maneuver cable into position
• mark length
• cut
• strip insulation
• temporarily slip on second lug
• mark position with sharpie across lug and insulation
• remove cable
• crimp second lug while aligning sharpie marks
• install braided sleeving and tubing
• permanently install cable

When complete, one end attaches to the ANL fuse holder.


The other end attaches to the second internal bus providing power to all of the fuses.


Next, we need to make a short cable to connect the second internal ground busbar to the external ground busbars. If you remember, this second internal busbar is not handling a lot of current. This is the ground point for pin 85 of all five relays. The maximum current with all five relays engaged will be less than 1 amp. Therefore, a jumper wire of 18 AWG from the internal busbar to the external busbar will be sufficient. But with that said, I chose to use 10 AWG wire strictly for the durability.

Cut a 3″ length of 10 AWG black wire. On one end, crimp on a heat shrink ring terminal with a 1/4″ hole. On the other, crimp on a heat shrink ring terminal with a 5/16″ hole. Use a heat gun to shrink.


Secure in place from the 2nd internal busbar to the external busbar immediately adjacent.


We need to connect the external ground busbars together. Cut a piece of 4 AWG welding wire about 4″ long, strip the ends, and crimp on a 4 AWG lug with a 1/4″ hole to each end. Use 1/2″ braided sleeving and 3/4″ heat shrink to seal.


Secure the two busbars together at the ends where the switch harness exits the enclosure.


At this point, the Bussmann RTMR is officially complete. However, for installation, we need to make two more cables:

• positive cable to connect the battery to the input side of the ANL fuse
• ground cable to connect the external busbar to the battery negative post

These will be cut to a custom length based off of your needs. The following picture shows where one end of the ground cable is connected to the external busbar.


The positive cable will connect from your battery to the input side of the ANL fuse holder or circuit breaker. I’m not detailing the specifics of these cables, because the length is dependent on your installation. But at this point, you should know the necessary steps to complete.

CONCLUSION

In this part, I have shown you how to build a Bussmann RTMR. I’ve detailed out to make the necessary parts and how to connect them. The final step is to install the enclosure in your vehicle, which I’ll outline in the next part, Part 6 – Installation.

 

Part 6 - Installation



This is Part 6 in an on-going series of tutorials that will teach you how to build a Bussmann RTMR fuse/relay block for your vehicle. Previous articles discussed parts, tools, and assembly for the enclosure. If you’ve been following along, then you should have a completed Bussmann RTMR fuse/relay block that is ready for installation.

In this part, there will be a modest amount of fabrication, and I’ll talk about switches in more detail. This will include detailed instruction on how to connect your switches, power supply, and grounds. I’ll be using my 2015 Toyota Tacoma for an installation example, so some details will vary with your vehicle. However, I’m hoping that after reading this you’ll have a basic understanding of how to install the Bussmann RTMR that you can adapt to your needs.

This part will outline the following:

• Switch Panel Fabrication
  
• Switch wiring
• Wiring harness installation
• Electrical connections
• Final installation

And as a reminder, I take no responsibility for damage, accidents, or injuries resulting from the fabrication or installation of any electrical modifications to your vehicle. You do so at your own risk.

Switch Panel Fabrication

Let’s begin by building the switch panel. For this project, I chose to install the switch panel in the overhead console sun-glass compartment. My 2015 Toyota Tacoma has two sun-glass holders in the overhead console, and I chose to install the switch panel in the compartment closest to the rear of the vehicle. This is a tight fit and prohibits the use of switch backs. Additionally, I haven’t tested if this setup would work in the other compartment, but I’ve heard that it should.

Parts used in this section:

Switch holder: Six Position V-Series Switch Holder

• Quantity: 1

Switches: Carling Technologies, Contura V

• Quantity: 5

Switch blank: V-Series Panel Plug

• Quantity: 1

Remove the overhead console with the sun-glass compartments from your vehicle. At a workbench, detach the sun-glass holder which would be closest to the rear of the vehicle, and set the overhead console aside. Using the switch holder as a template, mark the outline of the switch housing with a Sharpie pen.


With a Dremel tool, cut the hole. I found it easy to cut in two passes. First, lightly score the line, and then cut all the way through on the second pass.


The switch housing is easily snapped into place.


Finally, insert your switches in whatever position you desire along with the switch blank.


There is very limited space in the sun-glass holder compartment to accommodate the wiring. Therefore, we need to modify the backside of the overhead console to make more room. There’s really no accuracy here. Simply use your Dremel tool with a cut-off wheel and hack it. I removed as much as I could while retaining the mounting points.


From the inside, it should look similar to this.


Switch Wiring

The switches I’m using for this tutorial are made by Carling Technologies and were purchased at OTRATTW. They are Contura V switches with an independent lower LED and a dependent upper LED. This means that the lower LED is not controlled by the switch itself. Instead, this installation will show you how to wire the lower LED so that it’s controlled along with the same circuit as your vehicles dash lighting. Therefore, it will be dimming. The upper LED is controlled by the switch and will illuminate when the switch is on.

If you choose to use a different switch that either eliminates the LEDs or reverses the positions, then I suggest you read through this section and adjust accordingly. The terminals should be the same but in different positions.

This section will show you how to make a wire harness that supplies power and ground to all your switches as well as the signal wire to your relays. Study the following diagram of the back of a Contura V switch and familiarize yourself with the terminals. This diagram indicates the necessary wire connections, which we will make shortly.




Now that you understand how to connect one switch, it’s easy to wire multiple switches in a panel. By making individual wire harnesses for power sources and ground, these can be installed to jumper the switches together. This allows us to have a single source or ground wire for all five switches instead of separate power and ground wires for each switch. Taking a look at the diagram again, you’ll notice that each switch requires two power sources and two grounds. Therefore, we need to make a total of four wire assemblies that provide power or ground and that jumper the switches to each other.

As a side note, if you’re installing the switch panel in a different location and plan on using switchbacks, then the wire connections will be identical. Instead of connecting to the back of the switches, they will connect to the rear of the switchbacks. My suggestion is that you read this section and adjust accordingly after you understand the process.

Parts used in this section:

Wire: 18 AWG GXL

• Colors: black, red, brown, red/black, blue, green, orange, white, yellow
• Quantity: 19″ each color

Molex Mini-Fit Jr. connector: female, 10-position

• Quantity: 1

Molex Mini-Fit Jr. terminals: female

• Quantity: 9

Female Quick Disconnects: 20-18 AWG, 1/4″

• Quantity: 25

Heat shrink: 1/2″ adhesive-lined

• Quantity: 5″

Begin by cutting four lengths of 18AWG wire, 2 1/4″ long, for each color: black, brown, red, and red/black.


Strip each end of all wires 1/4″.


Then cut four wires 10″ long of the same color: black, brown, red, and red/black.


Strip one end of each wire 1/4″.


We will make all four wire assemblies before making any connections. So you can start with any color. Pick a color, and begin by twisting the 10″ long wire together with one of the 2 1/4″ long wires.


Crimp them together. I’m using 22-18AWG insulated female quick-disconnects. Technically, these are the incorrect size when twisting two 18AWG wires together. But they worked in my situation. If you find that they won’t accept the wire, step up a size to 16-14AWG connectors.


Next, using another 2 1/4″ length wire, twist the ends together as follows. Notice how I positioned the second wire. This is done so that when the assembly is connected to the switches, they install nice and flat without any twists.


Crimp on the second connector.


Continue in this fashion until you reach the last wire, where you simply crimp on the fifth and last connector. When complete, the assembly should look similar to the following.


With the exact same process, make three additional wire assemblies with the other colors. You’ll end up with four completed wire assemblies as follows:


Now it’s time to make your connections. The first connection will be to the lower independent LED. This is the light that illuminates when your dash lights are on. Begin with the brown wire to terminal #7 on the switches. Insert the terminal with the 10″ wire to the first switch and continue across to the additional switches. It should look like the following when complete.


The ground for the upper dependent LED is through terminal #8. Use the black wire assembly for this and connect to terminal#8 in the same manner as the brown, with the long wire connected to the first switch.


The power source to the switches, which illuminates the upper dependent LED and that sends power to the relays in your Bussmann RTMR, is connected to terminal #2. Use the red wire assembly and connect similarly as before.


Finally, connect the power source for the lower independent LED to terminal #6 using the red/black wire assembly.


The last terminal connection is for the signal wire that connects to the relays in your Bussmann RTMR. Cut five individually colored 18AWG wires 10″ long: blue, green, orange, white, and yellow.


Strip one end of each wire 1/4″.


Crimp a 22-18AWG female connector to each wire.


Connect the wires to terminal #3 of each switch in the same order as we did in the switch harness when building the RTMR: blue, green, orange, white, and yellow.


Now that the terminal connections are made, we’re at a point where a decision has to be made. If you recall from Part 5 - Building the RTMR, we made a long wire harness that plugs into the Bussmann RTMR and will travel through the firewall to the switch panel. Your decision is in how to connect that harness to the switch panel that you just wired.

If you’re using switchbacks, then you very well could wire the long harness to the switchbacks directly with jumper wires joining them all together. Another simple option is to use butt splice connectors. A final option is to use a connector of some sort, which is my preference so that the installation maintains flexibility and allows the overhead console to be removed in the future for any reason. My choice in connectors is a Molex Mini-Fit Jr. 10-position connector, and as this tutorial continues, I will outline the use of Molex connectors and terminals.

Begin by cutting a piece of 1/2″ heat shrink tubing about 5″ long.


Grab all the loose wiring together and temporarily slip on the shrink tubing. Cut the wires evenly so that they hang over about an inch. Afterwards, remove the tubing and set aside for later.


Begin by stripping each wire 3/16″ to accept the female Mini-Fit Jr. Molex terminals.


Crimp female terminals to each wire.


Using the heat shrink tubing that you set aside, slip over the wiring but don’t shrink in place yet. We want to insert the terminals into the plug first.


Insert the terminals into the Molex Mini-Fit Jr. female connector as follows, which has small numbers embossed on the connector for each wire opening. If you don’t have enough slack in the wires to insert the terminals, trim the tubing a bit and try again.

1. blue
2. green
3. orange
4. white
5. yellow
6. ——–
7. black
8. red
9. brown
10. red/black

Finally, use a heat gun to shrink. When complete, it should look like this.


Wire Harness Installation

Now it’s time to install the Bussmann RTMR switch harness that you made in Part 5.


This step involves routing the harness from your engine bay, through the firewall, up the A-Pillar and to your overhead console. We will also install the Molex connector that mates with your switch panel.

Parts used in this section:

Molex Mini-Fit Jr. connector: male, 10-position

• Quantity: 1

Molex Mini-Fit Jr. terminals: male

• Quantity: 9

Zip-ties: 6″ length

• Quantity: as needed

Begin by poking a hole through the firewall grommet in the engine bay. I used a coat hanger and then enlarged it a bit with a utility knife. Be very careful when doing this so that you don’t cut any existing wires traveling through the grommet. If you’re uncomfortable with the utility knife, you could use a small pair of cutters instead.

From the engine bay, push the switch harness that you made in Part 5 - Building the RTMR through the hole in the grommet. Once it’s through a few inches, you can switch to pulling it from inside the vehicle. Continue pulling it all the way through so that only the Weather-Pack connector remains in the engine bay. This means the two pigtails that branch off the harness are now on the inside of the vehicle.


Before routing the wiring harness up the A-Pillar and to your overhead console, we need to install the Molex connector to its end, because it’ll be much easier to do so now. Otherwise, you’ll be working with the harness over your head, and that can be difficult stripping wires and crimping small terminals. Also, leave the two pigtails hanging free under the dash for now. We’ll get to those later.

If you’re not using a Molex connector, you can install your quick disconnects or switchbacks at this point instead.

Begin by stripping all nine wires 3/16″.


Crimp Molex Mini-Fit Jr. male terminals to each wire.


Insert the terminals into a Molex Mini-Fit Jr. male connector as follows. You need to maintain the position of wires so that it mates correctly with the switch panel connector.

1. blue
2. green
3. orange
4. white
5. yellow
6. ——–
7. black
8. red
9. brown
10. red/black

After installing the connector, remove the A-Pillar cover and route the harness up to the headliner. Use zip-ties to secure in place where needed.


To route the harness under the headliner, I needed to remove the driver-side sun visor. This will allow the harness to easily slip underneath at the windshield. Continue routing the wire harness under the headliner and to the overhead console. The end should be sticking out of the headliner opening where the overhead console goes.


You can re-install the A-Pillar cover, driver-side visor, and overhead console at this point. The wiring harness should still be accessible.


Finally, connect the Molex connectors together and install the sun-glass holder. You may need to push the connectors and slack under the headliner before installing the sun-glass holder.


As outlined earlier, closing the sun-glass holder with the switch panel will be a tight fit. The removal of a large portion of the backside of the console should help, but installation can be made to work with a little massaging. I needed to bend the terminals slightly on the back of the switches. When closed, it should look like this.


Electrical Connections

The remaining steps inside the vehicle are to connect power and ground sources for the switch panel.


Parts used in this section:

Fuse tap: ATM Add-A-Fuse

• Quantity: 1

T-Tap Wire splice: 22-18 AWG

• Quantity: 2

Quick Disconnects: 22-18 AWG, male

• Quantity: 2

Fuse: ATM mini, low-profile 5A

• Quantity: 1

Looking at the pigtails that branch off your switch wiring harness that you installed earlier through your firewall grommet, route the pigtail with the single red wire to your under dash fuse panel. Using a fuse-tap, crimp it to single red wire. Choose an appropriate circuit on the fuse panel such as your 12V accessory outlets. Remove the fuse, and insert it into the primary slot of the fuse-tap. Insert a 5A fuse into the secondary slot. Notice the fuse positions in the following picture.

I cannot guarantee that all fuse-taps will be wired the same, so you can confirm the positions by inserting the original fuse into one slot and using a multi-meter or testing in circuit.


To complete, plug the fuse-tap into the fuse panel.


The other pigtail with the brown and red/black wires will supply power and ground to the lower independent LED of the switches, which will be dimmable. The brightness of the LEDs will be controlled via your dash brightness control, but these wires are not connected directly to the rheostat. Instead, we will tap off of an existing switch in the dash. For example, the VSC Switch is a good choice. Other options would be the Fog Lamp Switch, Downhill Assist Control Switch, or the Differential Lock Switch. Basically any switch lamp that is controlled via the dash light rheostat will work for our needs.

Take a look at the following schematic, which is a small section from the illumination schematic for the 2015 Toyota Tacoma Illumination. You’ll notice that each switch lamp has a green and green/white wire connected to it, which are indicated as “G” and “G-W” respectively. I’ve also circled in red the specific switch that I’ll be tapping into, which is the VSC switch.


If you remember from earlier, the switches are wired with two different grounds. One ground is for the upper dependent LED, which terminates at the Bussmann RTMR. The second ground is for the lower independent LED. The reason we need two different grounds is because of how the dash dimming circuit works. Let me explain.

One might think that the brightness of the dash lights are changed by varying the applied positive voltage to the lamps with ground remaining at 0V. If so, then lowering the positive voltage would result in a lower potential difference between ground and positive, thus resulting in a dimmer bulb. But this would be incorrect. Although the principle is the same, the approach is opposite. By varying the ground voltage instead of the positive voltage, the potential difference between the two changes similarly, and that’s what makes the bulbs dimmer. Think of it this way: the positive source will remain at 12V and the ground is capable of changing from 0V to 12V. With the positive source at 12V and ground at 0V, the difference is 12V, and the bulb is at it’s brightest. With the positive source at 12V and ground at 12V, the difference is 0V and the bulb is off. With the ground voltage level anywhere in between, the difference between positive and ground is what defines the bulbs brightness level.

Hopefully that gives you some understanding of how the circuit works and the confidence to splice into the vehicles OEM wiring. I’ll be splicing into the green and green/white wires for the VSC Switch.

Start be disassembling the dash as necessary to access the switch. Unplug the connector from the rear and remove any electrical tape or sleeving to expose the wires.


Use two T-Tap Wire Splice connectors to splice into the green power and green/white ground wires. To ensure you have a good connection, a multi-meter can be used to test conductivity between the splice and its corresponding pin.


Route your wiring harness pigtail with the red/black and brown wires to this switch. Strip and crimp insulated male quick disconnects to the pigtail wires. Then install onto the wire-taps. Connect the red/black wire to the green wire for a 12v power source, and connect the brown wire to the green/white wire to supply ground. Complete by plugging the connector back into the switch and reassembling the dash.


Final installation

There are only a few remaining items that we need to do before this project and tutorial are complete. As you know from Part 5 - Building the RTMR, we used Metri-Pack connectors for all accessories, which are waterproof. However, if you leave them hanging off the back of the Bussmann exposed to the elements, they’re not sealed and will be susceptible to corrosion and possibly a short circuit. But with an accessory connected, that circuit is protected and waterproof. For the remaining unused circuits, we need to protect them, and this is easily accomplished.

Simply insert cavity plugs into the ends of the mating connector.


Then plug it in to an accessory cable on the back of the Bussmann RTMR. Do this for each unused circuit and they’re protected..


Next, we need to make 4AWG power and ground cables. The length is determined by your battery location and specific setup. Just make sure you use adhesive-lined heat shrink tubing to seal the lugs to the cable. Assemble a red power cable to connect the battery’s positive post to the input side of the ANL fuse. Then make a black ground cable to connect the battery’s negative post to the 2nd external busbar under the bracket. Part 5 - Building the RTMR indicated exactly where this connection was made, but here’s the location once again as a reminder.


Once these cables are made, you can install the Bussmann RTMR. Locate and drill holes in the bracket, connect the six-way Weather-pack connectors, and install the Bussmann RTMR in your vehicle.


Installation is now complete, and you can safely install accessories that connect to your Bussmann RTMR as needed.


Conclusion

This tutorial has been a long journey. If you made it this far and you successfully built and installed a Bussmann RTMR in your vehicle, congratulations! Not only are you rewarded with a successful installation, you learned what tools and parts are needed to build a Bussmann RTMR, and you learned how to assemble and install the enclosure. You also gained some theory and basic knowledge of electricity regarding switches, relays, wire gauge, etc. Consider all of this valuable information, because if you’re ever out on a trail and are having some sort of electrical issue with your accessories, you should now be confident and skilled in solving the problem.

 

This is going to be good
Although I have an sPod, it's nice to learn about other options.

 

Wow tons of info! Sub'd for later

 

So much win here! This is on my list of tings to do! WOW!!!

Mike, you are amazing!

 

Thanks! Subd for future use!

 

I've been working with Mike over the last few weeks (month?) and built mine using his tutorial. The install will take place sometime this month after I get my custom plate fabricated.

Kudos, Mike! Great work.

 

Holy Crap! That is an extensive write up. Great job and thanks for this!!!

 

Thanks guys. This was a shitload of work. And I really have to give thanks to Chris (kitsym) for his valuable feedback. We started conversing a while back, one thing let to another, and he's been following the tutorial before I published it here. Along the way, he gave me great feedback that I incorporated into the tutorial.

 

I also want to kind of "apologize" for the large number of photos. It sure makes the page loads a pain, but it's a necessary evil.

 

TLDR; just quote someone else.

Great job OP. I'll flip through this eventually. I have already built my own box, so I might have something to add. Maybe you seem to have covered everything.

 

I reported this thread!











And asked the mods to "sticky" it!
Excellent write up!
@tacozord

 

Beyond impressive write-up, saving for a rainy day.

 

Are you kidding? They are critical, and the more, the better.

 

holy crap...

 

Sub'd