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

I believe the grounded wires are gathered internally and there is only one long main ground wire coming out, shown in photo. I'm guessing I will not need the buss bar for the relay side, possibly for the fused side... Looks like all I will need in the beginning to install is the positive wire from the breaker to the battery since the one attached already to the Bussmann will go to the other end of the breaker.

 

I'm thinking you still need to ground all 10 circuits as it looks to me like the black wires only ground the signal side of the 5 relays. This is based on the following assumptions of things I can't see.

4-pin relay installed right side up
Pin 30 powered from red fuse jumper
Pin 85 grounded through black wire
Pin 86 switch wire
Pin 87 accessory wire
Power applied to switch wire travels through relay coil to ground (pin 86-pin 85) and closes relay connection to allow current to flow from the fuse jumper to the accessory(pin 30-pin 87). There isn't a ground connection for the accessories yet.

 

Thanks for this. I'll try and get some better pictures. This helps a lot.

 

You're welcome. I'm doing this as an excercise to help me better understand this stuff, not because of any extraordinary knowledge. If you can get to where you know how yours works then you'll be caught up with where you'd be if you put it together yourself. In other words, verify anything I suggest.

 

I agree. I have a basic knowledge and safety in mind but the setup and install varies from Bussmann to Bussmann. Learning a lot from this.

 

Here are the photos. Hopefully this will clear up what is needed for the install.

Also: Taken from the first post on this thread.

• 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.

 

I dont see anything to change what I wrote above. The relays are installed right side up which confims the pin layout(not that it should make any difference since relays are non polar and there's no relay buss) it appears the relays grounds are all spliced together to a single 10awg wire which while overkill for the .5A needed to trigger all the relays simultaneously(could have just used 18awg) is inadequate to carry the 80A of the bussman to ground which further suggests it's not intended for that. To hook it up I would:

Supply the relay switches with 12V(ignition switched source (fuse tap)or from one of the 5 non relay fuses if you want "anytime use").

Connect each accessory to one of the 5-10awg color coded wires with either a 10awg return to a common buss bar or grounded to the frame(upgrade the battery ground if you go this route).

Connect each of the fuse only wires to its accessory with a ground return to a buss bar or frame.

Connect the red 4awg to the 80A breaker or fuse and the breaker/fuse to the battery +.

Connect the black relay ground to battery -.

Connect the ground busses to battery - with a 4awg cable.

I prefer the idea of using buss bars and ground returns simply because the buss bars are made with non corroding connectors and the frame isn't(in fact, you need to scrape off whatever protection is there to get a good connection). The extra ground wires are a hassle but one I'm willing to deal with.

 

The frame ground issue is one you'll get different opinions on. At a guess, I'd say this set up favored frame grounds since the accessory wires are gathered rather than separated but you could easily slide off the loom to separate them and still set it up like the op, it's up to you. Maybe contact the seller and see what he had in mind. Possibly nothing more than this was the easiest way to put together an rtmr.

 

I appreciate all this. I'll be referring to this come install time for sure.

 

I recently built another Bussmann RTMR that connects to my auxiliary battery and is used for accessories in my bed. Anyway, it's different in design, but all the principles stay the same. You can check out more details on my build page here.

 

When I purchased my FlipPac camper shell, which was used, it already had a dome light installed. I temporarily connected it to a spare fuse on my 1st Bussmann RMTR that I built a couple years ago knowing that I'd ultimately be installing an aux battery and another RTMR. For this temporary setup, I didn't connect it to a relay or anything. I simply used it to provide power from the RTMR back to the dome light in the bed of the truck and used the integrated switch on the dome light.

Now that I've installed a second battery and built another Bussmann RTMR dedicated to bed/shell accessories, it was time to connect the dome light permanently. But I also wanted to modify the circuit to accommodate two switches to control it. I never liked the fact that when I wanted to turn the light on, I either had to crawl into the shell or open the driver-side win-door. This was really inconvenient. So I wanted two switches, one at the rear of the truck and another at the light itself. The following circuit diagram outlines the wiring.



This is called a three-way circuit and many people might be familiar with it when two switches control a hall light in your home. There's typically a light switch at either end of the hallway and these switches are called double-pole-single-throw switches or DPST for short. I purchased my switches from OTRATTW, part number #V4D2UXXB-00000-000. The specific switch I purchased didn't come with rocker covers, so I purchased two of those separately, VVPZC51-5BA1.

This is the switch wiring diagram that OTRATTW provides.


In the following image, which shows my Bussmann RTMR wiring and connections, the white plug on the right connects to the switches at the rear of the vehicle. Two of the wires are used for the dome light switch, and a third wire supplies power. The white plug at the top left goes to a new switch at the dome light. Notice that there are three wires. The brown and white wires connect to the terminal block and continue to the switch at the rear of the vehicle. The blue wire connects to pin 86 on one of the relays in the RTMR. And finally, the black plug at the top left connects to the dome light with two wires, black to ground and red to pin 87 of the relay.


Here's the switch panel at the rear of the vehicle.

Here's the dome light and secondary switch. In order for this system to work, the original switch that is integrated in the dome light remains on at all times. This was the easiest thing to do instead of replacing the light or re-wiring the dome light.


I used a Hammond 1591DSBK ABS project box that I purchased from

$12 Hammond Manufacturing 1591DSBK STYRENE PLSTC CASE

Amazon for the switch at the dome light.


With it installed and working, I love it. I can turn on the light from the rear without crawling in, but when I go to sleep in the FlipPac, I can easily reach down and control the light from the secondary switch. I'm chalking this mod up as another favorite. It's rather easy to do, and the payoff is better than expected!

 

Question...
If you’re hooking up (2) 10A items to 1 fuse location... would you just put a 20A fuse in that slot then?

I’m curious, gonna run the items to separate block spots at 10A a piece but for future knowledge...

 

Nope! It doesn't work that way. The fuse is not in place to protect the accessory or accessories. The fuse is to protect the wire. That's it!

So...you first find out how much current the accessory or accessories need. Then you select a wire gauge size that can handle that much current. Ideally, you want a wire that can actually handle more than the required current. Then, you select a fuse to adequately protect the wire in case of a short.

 

Ohhhhhh I see.
I was always under the assumption that your fuse was there to protect whatever it is you're running power to so you don't destroy that, instead of say, ruining your alternator, when you cross the jumper wires... your ALT fuse blows instead

So the fuse amperage is based on the gauge wire you'll be running, and how far you'll be running it, then you pick the fuse size?

 

Yup! You got it.

 

Don't know if you got this figured out yet, but I have the same one and set it up below. You need a bussbar for the grounds coming off the accessories (I tied the one from the RTMR to this, then one lead to the battery), and the fuse that came with it (I used a separate dual fuse for my stereo as well). I used a terminal block as well for easy connection of future accessories.

 

Thanks! Will be finding time to order the cables. Think I have the right sizes now. Will be looking back at this during hook up. Don’t know what a terminal block is though. Will look it up.

 

Terminal block is simply a block with isolated pairs of terminals unlike a buss which has all the terminals in common. You would have each accessory wire from the rtmr end in a ring connector to one side of a designated pair and the wire to the accessory with its own ring connector on the other. Just another way besides using the more expensive individual connectors in the op to pre wire all the rtmr bits so all that's needed is the correct fuse.

 

This is a terminal block:

Blue Sea 12 circuit terminal block, part #2512
https://www.bluesea.com/products/2512/Terminal_Block_30A_-_12_Circuit


This is a bus bar:

Blue Sea 150A 10 gang Bus Bar, part #2301
https://www.bluesea.com/products/2301/Common_150A_BusBar_-_10_Gang



The difference is that the bus bar makes all the connections common whereas the terminal block allows several separate connections. In the image above of the terminal block, it allows twelve distinct pairs of connections. It's used for convenience to connect pairs of wires together.

Look at the following image where I've used both. The bus bar is used to tie all my grounds together. The terminal block allows me to connect different circuits from the Bussmann RTMR to the accessories.

 

What is the average cost to build one of these Bussmann RTMR fuse/relay block?

Just the Bussmann not all the other items?