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

The RFRM will hold, I believe, something like 12 relays, it's huge. Which I presume is why they don't make a bracket for the OR that can hold it and a CB. I might just stick with the RTMR, I dunno. I'm not sure if I'll ever need more than six slots.

 

But they've got a bracket that holds the RFRM and a breaker for the non-OR models. Of course, I don't know what the space difference is, just that there's different brake system components or something.

Also, I believe the RFRM has 10 relay slots.

 

Rtmr has 5 relay slots and 10 fuse slots. Another thing to consider is the 30A per circuit limit. If you think you’ll need any higher current circuits than that you’ll need both a separate fuse holder and relay each rated for the higher current. Micro fuses only go up to 30A. I went ahead with the Bussman but fused my compressor separately.

 

That's a good point. I do plan on eventually adding onboard air as well. I see the ARB one draws 50A under load. Is there any version of the Bussman that allows a larger fuse than Micro?

 

Well, I should correct myself and say that some of them draw that much, not all:

https://www.arb.com.au/assets/air-lockers/6-07.pdf

 

Not to my knowledge. There are other fuse/relay combos that use the larger ato fuses. These guys
https://www.amazon.com/s?k=ato+fuse...bmt=be&hvdev=m&hvqmt=e&ref=pd_sl_27hag6pw7q_e
use them and the metric pack 480 terminals in them are rated to 48A but for 50A draw I’d consider either a separate ANL fuse/holder or a dedicated 50A breaker. You can also get the male half of those fuse holders and have 48A capable connectors.

 

I was watching an install vid for a ARB dual compressor, and it looks like the wiring harness included with it includes a relay and a fuse already wired up, so maybe it wouldn't be necessary to do a whole new block, bracket and all that unless you had more than a couple things drawing that much. I think I'll just put in the Bussmann RTMR for now since things like a winch and a compressor are coming later on anyway, I'll figure out some sort of separate power distribution for those things later.

 

I believe the ARB wiring harness has an integrated relay.

https://www.tacomaworld.com/threads/rtmr-wiring-to-arb-locker-and-compressor.392710/#post-10829796

You need at least 8 gauge for 50 amps and for a rear mount location like I’m planning, 4 gauge. I have a dedicated circuit breaker, went with 60 instead of 50 since I’ve read it can pull a little more than 50 at startup.

I am mid flight on my high current distribution center on the passenger side using a GTFO compressor bracket (capacitor underneath, circuit breakers on the side).

 

Hey fellas, now that the weather is cooling down I want to finish this project. My tray is built, but I still need to make my accessory cables and battery connections. I grabbed some scrap wire from a project at work and am wondering if anyone can give me a thumbs up or down on it. This would be in lieu of the welders cable that everyone is using for the 100A breaker and direct connections to the battery. Pics below.

<edit>. Looks like it’s 1AWG, so that should be plenty of bandwith.

Can anybody speak to whether this is ok for the engine bay? I’m not sure about the temperature resistance of the coating.

 

90C seems a bit low. I’m not really comfortable recommending that usage even with high temp wire loom to surround each piece. High current cables with inadequate insulation just strikes me as a recipe for disaster.

 

Appreciate it.... that’s what I was looking for. These are from equipment at 125A 480V 3 phase. 90C converts to 194F. I doubt it gets quite that high under the hood, but 150+ for sure. Probably best to order the recommended wires then.

 

Exhaust pipes are a lot hotter than the block temp and these installs are usually closer to those than they are to the radiator. https://mechanicbase.com/engine/how-hot-does-an-exhaust-pipe-get/
Edit- there’s a good reason for using high temp insulation in the engine bay.

 

breaker will fit... just need to drill 2 holes
4

 

If I look up ampacity charts for 4awg wire it says 70 amps but everyone on here seems to be using 80 - 100 amp circuit breakers. Wouldn't the breaker have to be less than the amp rating on the wire so it breaks before exceeding the amp rating of the wire?

 

I'll take a quick stab at this. I think the primary concern is resistance rather than heat here? Because within the engine bay we'd be using thermally protected cable and subject to external heat anyway so the temperature of the wire itself is a lower concern than it's resistance? I'm sure someone with more working knowledge can step in with a better explanation.

Based on the charts which take distance into account, a short 12 inch jumper of 4 gauge is well within operational range of any reasonable circuit breaker. Why use 4 gauge instead of 2 or 1/0? Most likely because it's smaller and more flexible, also more easily available and lower cost.

 

Just be sure to get copper wire instead of copper coated aluminum. CCL is much cheaper but doesn’t carry as much current for the same wire size and I’d be surprised if everyone knew there was a difference. ​

 

Would it be a good idea to run ignition power into a relay so that it works almost like a switch kind of telling the relay to turn on for ignition power that way I wouldn't be overloading a circuit as I do plan to use allot of mods with my RTMR. Is this a good idea? And if so what would be the best fuse to tap for ignition power inside of the cab?

Also I bought the following tools:

$18 iCrimp Open Barrel Terminal Crimping Tool for Molex Style DELPHI AMP TYCO Deutsch Terminals Crimper, Molex Crimping Tool,24-14 AWG

https://www.amazon.com/gp/product/B07476C1LD/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

$18 iCrimp Crimper Tools for Delphi APTIV Packard [Weather] [Pack] Terminals Metri-[Pack] Connectors for Sealed Terminals

https://www.amazon.com/gp/product/B071KFLY43/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
are these the correct crimping tools?

Also I have a relay for front off road lights (1), and a separate relay for rear off road lights (2). A relay for switched ignition power to power my interior accesories (3), and a relay to control my interior led light kit (4).
Any way to not use all of these relays? I have three switches in the interior of my truck I plan on using from channel 4x4.

 

You can tap into the 'key on' signal at the EFI relay under the hood. For clarity, you want to tap into the voltage of a circuit as this is equivalent to reading out the signal state. Tapping into the power of a circuit implies tapping into the current, which is a different thing. Same as reading the pressure of a pipe vs. tapping into the flow rate of a pipe, which is diverting the flow.

 

You can use the Bussman to replace all 4 relays and have one left over for another mod. The Bussman relays will draw power from a max 80A fuse or breaker connected to the battery. The switches that activate the relays can draw power from either an always hot fuse tap(door lock fuse) or ignition hot fuse(ACC). In either case no current flows through any relay unless it is activated.

 

I have mine built. My lighting is all LED. Ditch, hidden light bar and LED bed lights. I have the 5 fuse only posts available. I want to add a 7 wire trailer harness. I do not have a trailer but wanted to go the whole nine. The fusing on the harness is a total of 75 amps with the fusing (trailer breaks, 12v to the trailer plus lights). Per the OP the Rtmr should handle this. Do you think I can add it to the fuse only side as long as I don’t turn on the lights while towing with Trailer brakes and such? Should I just add dedicated fusing for the tow system?