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

Bad connections suck. I just spent several days chatting with another member tracing a similar problem. Lots of good continuity checks but no light. Turned out to be a bad connector pin-to-pin connection. Sometimes it’s a bad crimp, sometimes a more facepalm issue.

 

So I replaced all the connections and have no electrical current problems. I got a meter and it appears I have electrical flow to the Bussman plug, but I still have no power to the lightbar.

 

It sounds like you're in a typical 'problem solving' situation. This is almost always the case, even for myself. When designing something like this, I was constantly running into issues. But that's part of the journey and why I test every step of the way during assembly and install. To solve your situation, you have to think about this logically, change or look at one variable at a time, and test. Then test some more. And test yet again!

So, test one...verify your power source! This should be easy enough with a volt meter.

Next, verify that the light bar works, which I think you've already done. Connect it directly to the power source. Eliminate the Bussman, switches, connectors, wires, etc. In fact, don't even use the truck. Hook up the light bar directly to your battery or even a different power source that you've also verified. I'm assuming it's a 12v source that's needed? You haven't indicated the manufacturer or model number of the light bar. What do the instructions say? What is needed? Look at the specifications and make sure it's compatible.

Next, verify that your switches are properly working. Using a continuity meter, test the switch when it's engaged. This can actually be done at a workbench. Then, using a volt meter and with the switch in circuit, test the voltage at the switch on the input side. Then engage the switch and make sure that the voltage level is the same on the other side. Then test voltage all the way back at the Bussman. You want to make sure the switch is doing what it's supposed to be doing, which is supply a low-level current to the relay. If that works, go to the next step. If it doesn't, find out why. Loose connector? Broken wire? Incorrect wiring?

Next, test the low-current circuit of the relay. Check continuity of it; this can be done with the relay on the bench. Then plug the relay into the Bussman and make sure you have voltage on the input side. Engage the switch and make sure you have voltage on the other side of the relay. If good, move on. If not, try a different relay. Is that one bad? Or do you have it wired up incorrectly?

Next, test the high-current circuit of the relay. First test continuity when the low-current circuit is active (when you do this, no wires are connected to the high-current circuit at all. Simple way to do this is by disconnecting the power source that goes to the high-current sides of all relays.). Then connect the relay properly and test voltage on the input side. If good, engage the switch for that specific relay(which provides current through the low-current circuit and engages the internal switch of the relay to allow current in the high-current circuit) and test voltage on the other side of the relay for the high-current circuit. If that's good, then go to the next step. If not, maybe the relay is bad so try a different one. If that doesn't solve it, then verify that you have it wired up correctly. Inspect the connections, the wires, etc. Is the relay installed backwards? Once good, move on.

Finally, connect the light bar to the high-current circuit of the relay. If everything above works, then this should work. It's only two wires...one of the positive wires to the high-current circuit of the relay and the other wire to ground. You're only testing one color of the light bar at this point. If that works, test the other color. Finally, connect them both to separate relays and you're done. If this still doesn't work, check your connectors yet again. But honestly, it should work by now. You've eliminated every variable up until this point, at least what I can think of while I'm typing this.

The key take-away here is to slow down, think, and apply logic. This isn't rocket science. If you understand the basic layout of what you're trying to do and you've drawn a simple circuit diagram with all the components, then all you have to do is look at each of the individual components and test them independently to find the problem. These include the power source, the load(light bar), connectors, wires, switches, and relays. A problem can occur at any of these locations and it's up to you to figure out which one. But it can also occur with simply how you've designed the circuit. It may come down to having it connected wrong because you may not understand how it's actually supposed to be. I'm not trying to be disrespectful here, but simply being honest. Look at where a problem can possibly be, then prove that it's not a problem until there's nothing left to prove.

Anyway, I suspect that the problem lies in something simple that you'll probably hit yourself in the head once you realize what it is. Keep at it and you'll find it. It's happened to me plenty of times!

Best of luck!

 

Ok, bear with me here (and my massive lack of brain power)....I overloaded the circuit. I blew the first 3 fuses and they were the last thing I checked before telling myself I was going to pull everything out and rewire it. MASSIVE facepalm. I replaced them with 10s and everything works!

 

haha I knew you'd hit yourself in the head. Can't tell you how many times I've done that as well.

Anyways, congrats on solving the problem. Looks like I overlooked advising the simple fact of checking the fuses as well.

 

Thanks for the help though!

 

What the wattage on each of the light bar circuits? And the wire gauge? Previous fuse ratings?

 

Wattage: 10-30 DC
14 AWG wire

 

So less than 3A max and way under the max for that wire size.

 

I've read through the OP a couple of times, and made it all the way to the end here. I think this is what I want to do, but I haven't decided 100%. It isn't the time or effort, this looks like fun to me. It's the initial cost.

If I were to buy

$29 Delphi Packard Five-cavity Wide-range Crimping Tool 22-12 AWG / 24-14 AWG

this for crimping the tangs, what else would I be missing? I know it obviously wouldn't cover the 4AWG cables. Would it not work on the weatherproof connectors?

The other thing I'm looking at is that I want to start on this well before I have or have even decided on all the things I want to hook up to it. I like the adaptability, but obviously there's only five relays. I'd have to be careful I don't exceed that if I buy/make a mount, get all this done, etc. If I'm looking at scene lights, something like the Baja designs rock light, it says they use 4w/.40A. Could I do something like wire four of these up together, run it off one of the fused connections without a relay (interior switched)? That would open back up a relay slot.

My thought would be to do something like this, but I'd have to scale it back a bit or do a second one. All I have right now to install is a winch (breaker/quick disconnect to batt) and the bumper light bar. I was thinking I could temporarily hook the light up until I get this sorted out.

 

You can get the RFRM (or something like that) which doubles the number of relays available to 10. That's the route I'm going because I share your thoughts about running out of relays. Disadvantage is it ups the cost and it's harder to find a tray mount for it.

 

I finished my RTMR build just before Christmas. I had similar concern while designing my setup, but after a lot of research I came to the conclusion that a relay for something like the BD rock lights is a bit of overkill. They each pull 0.4A, so even 4 wired together is only 1.6A. Ensure you use high quality switches, not the cheap Toyota push button style rated for 3A, use something like Carling Contura II or III switches rated up to 20A. I used 4 relays for my 30" light bar, a pair of BD S2 Pros, and 2 pairs of BD S1s, which is a ton of light. Everything else is wired to the fuses (12v power and 3 LED strip lights in my canopy).

 

Consider getting a single stage crimper:

$33 iCrimp Weather Pack Crimp Tool for AWG 24-14 Crimping Delphi APTIV Weather Pack Terminals or Metri-Pack Connectors- Crimp Terminals and Seal In ONE Cycle with Locator & Removal Extraction Tool

https://www.amazon.com/dp/B07GB698KV/ref=cm_sw_r_cp_api_glc_fabc_aUCbGbQA3YF4C?_encoding=UTF8&psc=1

It makes very quick (and consistent!!!!) work of metri/weather pack. I used 12 ga on my build and it worked great. 10 ga “worked” (I did a few test crimps with 10) but I had to mess with it a bit. Just my 2 cents if you’re looking for a quality tool on a budget. You’ll fly through the project pretty quickly using a single tool.

I assume you already have an insulated crimp tool (cheapo harbor freight). Outside of lug crimpers for the battery + ground feeds it’s all you need unless you really want to get a specialized tool for 10 ga.

 

So this replaces what I suggested or supplements it? Some of the terminology is a little bit confusing as to what goes with what.

I have quality wire strippers, and a couple standard wire crimping tools.

 

Replaces it. The reason there’s two crimpers in the instructions is because the main tool only works well up to a certain wire gauge size. However, the main tool you’ll be using crimps the seal of that larger gauge just fine. So what ends up happening is people buy one tool to crimp the conductor strands of the larger gauge only (as it’s too big for the main tool), and then switch back to the first tool to crimp the seal. It’s up to you what gauge you’d like to run — if you’re running 12 or 10 it’s doable with a single tool. Just check your work.

 

It's the mounting that concerns me about going bigger.

I do want to keep things as stock looking on the inside as possible. I was planning on the push button for everything I can get away with.

 

The wire crimp does the wire but the second crimp has to include the silicon seal and because of how soft those seals are it doesn’t really help with holding the wire in the terminal. This reason rather than any connectivity concerns is why I solder the terminals. It also means you really need the right size tool to crimp the seals or they split.

 

If you’re going to use Molex or some sort of open-barrel style connector in the interior you can also purchase an inexpensive single stage tool for that:

$16 Knoweasy SN-28B Wire Crimping Tool - Terminal and Wire Crimper for 3.96mm, 2.54mm, 2.5mm Pitch Dupont, JST XH VH Connectors - AWG 23-17/0.25-1.0mm² Crimping Tool

https://www.amazon.com/dp/B07BV1YP3M/ref=cm_sw_r_cp_api_glc_fabc_igDbGbXYQ61M2?_encoding=UTF8&psc=1

What you do inside the truck is personal preference (some people just use standard insulated crimp terminals, I guess). If you have a simple crimp tool for insulated terminals, something for sealed terminals, and then something for open-barrel you’ll be set up for almost anything in your truck (OEM connectors included). If you get fancy and start going the Deutsch route your wallet will hurt a bit.

 

OK, so the two crimpers mentioned, a way to crimp the large gauge wire, and the materials. I should be good, right?

 

I have a mount for the larger RTMR. Accidentally bought it and couldn’t return it