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

Super rough atm, but using Fusion 360 for the beginnings of a mounting panel design.
RTMR and 5 gang busbars were on grabcad, but I just drew up the 80A breaker.


We're slowly making progress. Kind of a background project at the moment.
Mouser has a few items in my order on backorder: May 2021 / Jan 2022... So hopefully those status' and dates change soon...

 

If all the switches(or almost all) use the green plugs I depin them and remake them with daisy chain for the 3 common wires then use whatever molex can carry those plus the switch output wires. A 3-gang switch bank would have a 6-pin molex, 4-5-gang an 8-pin molex, etc. basically turns the green plugs into switch backs the way the op described.

 

I use the time spent on waiting to mull it over but I wish it knew about that Digikey link a few years ago since it definitely organizes better this way. Also read up on dash dismantling, door wiring, or any other areas I need to access to ease the process.

 

If space is tight you can double up the ground busses on the Bussman screws.

 

OK, I think what I'm going to do at the switch locations is use a heat shrink inline crimp and take one 18ga into three 22-24ga before the Molex. That will keep things nice and tidy, and the ends of the wires from the switches and daisy chains can plug straight into the Molex. From what y'all have told me previously, the 22ga or 24ga wire should be able to handle the ACC signal load for the switches, yeah?

It would obviously be easier to use the 18ga stuff I already have, but I doubt there's a readily available butt splice that can do 18ga on one end, and something like 12-14 ga (when they are all wired together) on the other. But I could try. Oh, wait, I could strip the single wire longer and double it up, couldn't I.

 

It’s easier to crimp a small wire into a big terminal than vise versa but that doesn’t really apply for terminals that have bonded or heat shrink insulation already applied. For that reason I prefer uninsulated terminals that allow access to the crimps which I can heat shrink as needed. Soldering is a belt and suspenders approach but I’ve never pulled a wire from a terminal if it’s been soldered and it happens all to easily if not. It also assures maximum connectivity.
Doubling up works and sometimes you can resize the crimp to collapse on a smaller wire, just compare the different wire size terminals for any given connector type. A few seconds with a Dremel wheel and boom. PITA to get 10awg wire to fit an 18awg terminal but no big deal to get a good connection with 18Awg wire(or 2!) in even a 10awg terminal so if you have several wire sizes and are a cheap sob just buy for the largest size. Obviously it’s best, easiest, fastest to have and use the proper sizes but in a pinch, can do.

 

As a test, I did have good results twisting and crimping three 18ga in a 14-16ga butt. I may try to grab a 10-12ga and see how that works. I have plenty of pink 18ga that I wasn't planning to use for now.

This is probably going to be an easier problem to solve than I originally made it out to be.

 

These look really nice, what’s the final cost on the parts and do you estimate the build time to be?

I was considering one of the switch pro units but not for $600 and I’ve seen a cheaper version for half that but with less features. It does have a relay box.

 

Well, all told - its about a break even. If you add in the aluminum mounting bracket, all the connectors, wire and the tools - its around $500. But - a 2nd one would be far cheaper - so, it might be a good idea to build two of them - and sell your buddy one for $300 to cut costs. The whole purpose of a bussman RTMR is you can replace parts and relays when they burn out - and you decide how to build it to your specifications. The Bussman allows for multiple configurations - so its really more of a DIY project. The Switch Pro is nice for what you pay for - but yes, its a convenience item. If you have the patience to build a bussman RTMR, you won't regret it - but - ask others if they want to pitch in and build 5 of them at once and sell off the extra ones. This way its more cost effective for you.

 

A good chunk is the wire and connectors to hook it up to anything and you need wire to make up the RTMR so it makes sense to buy for all your usage(a 100’ goes fast). The tools you will continue to use for each harness you make for accessories so they aren’t a one and done purchase. The RTMR itself is less than $50 but you need fuses, relays, and terminals for it as well as for the connectors, then buss bars, a breaker, a mount panel and 8mm bolts. It keeps adding up.

 

Gotcha. Thanks so much for that, really appreciate it. Definitely makes sense to build a few at once to mitigate the cost.

The guys going the switchpro route were still using a terminal block to be able to trouble shoot stuff on the road.
I only have a few lights now but don’t want to make a mess and rats nest.

 

That was my thought as well.
I have no accessories at this point, but pre-wiring the truck for them so all I need to do is build each harness run from the bussmann to the respective accessory, remove a switch blank from the panel in the interior, and plug in a proper switch. Keeps everything clean and OEM looking wiring.

 

I probably am in for $550 and I only bought two tools. I looked into building more, but even selling them at $300 wouldn't have netted much profit, because I didn't feel like buying 100-ft spools of wire among other things.

It was fun, though. Learned a lot. I could probably troubleshoot anything electrical on the truck, now. I did buy some personal use spares, like a full five extra relays. They're cheap enough to have around.

 

I have Switch-Pros 9100 and also have learned to crimp and build my own harnesses. I don't see a massive cost differential nor is there a significant difference in install time/complexity (both are non-trivial, both are well within the grasp of anyone who can take the time and proceed methodically).

The big upside I see to the Switch-Pros is the compactness of the control module (8 fit in the space which only 4 small OEM style switches can fit) and the programmability (bluetooth, ease of re-purposing a circuit).

The big upside to OEM style switches with a RTMR or any other fuse/relay block and custom harness is that it looks more OEM-like at the switch itself. I'm not completely in love with my Switch-pros command module. But the BT is a nice feature, If you were in the bed and want to fire up a circuit you can do so with a phone instead of having to pre-place additional trigger switches in various places.

If the Switch-Pros could accept a total or 4+ input triggers (dome, drl, high, low, maybe hood) in addition to parking and ignition, I'd be an even bigger fan. And if it could feed OEM style switches (stowaway command module) I'd be completely thrilled with it.

A waterproof bus bar would be nice too, don't see why bluesea doesn't make something like that, seems so trivial. Some rubber seals for various wire gauges, a clear plastic cover, so easy to do.

 

The multiple functions of the SP unit was why I was considering it, like the ability to strobe, etc....I guess that’s the programmability aspect.

it seemed like a lot of people were still using a blue sea fuse block and said it was to be able to do trouble shoot and rail fixes in the event the SP failed.....which is a lot of money but I guess cheaper than the other unit that was more than the SP.

 

Blink modes aren’t a selling point for me and no one single unit was going to do everything I wanted but the Bussman is what I chose as the centerpiece to organize around. It’s not my only spot for either fuses or relays but corresponds to the main panel in a house that can have sub panels elsewhere.

 

Does anyone have extra materials to build a couple very short (max like 8-9”) battery cables? I’ll pay, obviously. I just need someone to cut + crimp — I’ll take care of looming and heat shrink. Figured I’d try this sub as someone might have some extras. I left my large lug tools/materials in storage while I moved. Didn’t think I’d need them. Just let me know, thanks!

 

I have the cable in red but no lugs..

 

^^ I got this one, I owe Kyle anyway.

 

I recently redid my entire panel work in my current Toyota. This time I wanted to avoid the semi-rats nest look and went with a Deutsch bulkhead 16pin 10-12awg connector and a Shrockworks double rtmr mount. Threw the 2x 5pin weatherpacks in the garbage. About as clean as I have ever made it look. Still need clean up some slag over by the firewall. Got some Deutsch connector mounts to actual affix them rather than let hang.