Wiring electric trailer brake controller

[colinnwn]

I'm in the process of doing this, and the red wire (brake sense) says to "wire into the cold side of the stop lamp switch or brake light." Most people say to find the brake switch wire under the dash and tap into it.

 

With the very small wires under the dash, tight wire routing, and limited access, and since I'm already running the blue electric brake wire to the connector at the back of the car, I was thinking about just running that red wire back with it, and tapping into the brake light wire right before the box for the 3 to 2 wire trailer converter.

 

Has anyone done it this way, or have thoughts one way or the other?

 

Thanks.

[colinnwn]

Ok I think I found a good place to tap into it based on just the FSM without seeing how hard it will be to get in there. On my 2001, the ACSD (cruise control box) is behind the driver kick plate. In the connector going into it, on the bottom left 2nd to the last position (23) there should be a green/yellow stripe wire that goes to the brake switch.

 

If my splice were to fail, the cruise control wouldn't kick off automatically when braking. That isn't ideal, but better than the anti-skid brakes not engaging. I'm hoping this isn't a tiny gauge wire, since my brake control box has a 16 ga pigtail (and recommends 16 ga wire) for brake sense. I don't understand why it would need to be that big for a sense wire.

 

The other option is to splice into terminal 1c on the SMJ which is also a green/yellow stripe wire going to the left stop lamp. This might be a better location, because if my splice fails, the only thing that would happen is the left stop lamp wouldn't light up. But I can't find the SMJ terminal layout in the FSM. I'm doing OCR on it now, but it is going to take several hours. And from what I recall the access to wires around the SMJ is much tighter.

 

I guess I'll get a better look tomorrow afternoon after work.

[Slartibartfast]

Odd that it suggests a thicker wire--like you said I'd expect that connection to be for sensing rather than supplying power. If you have an ammeter, you could rig everything up in the back of the truck with jumper leads, hit the brakes, and see what the actual load on that wire is to get some idea for what size of wire you need. But rather than dig into the cruise control harness or the SMJ, why not just run it to the brake switch itself? It's not that far away and unless the R50 hid it better than the WD21 did, it shouldn't be that hard to get to.

 

Provided you do the splice properly (just say no to suitcase connectors), and the brake controller doesn't burn up and short out, you shouldn't have an issue with the circuit you're tapping into. That said, if I had to choose between no ABS and the cruise control making the engine fight the brakes, I'd take no ABS any day of the week!

 

[Citron]

Cold side? Never heard that before.

[mjotrainbrain]

Cold side? Never heard that before.

 

Maybe a poor translation meant to mean negative?

[colinnwn]

 

 

Odd that it suggests a thicker wire--like you said I'd expect that connection to be for sensing rather than supplying power. If you have an ammeter, you could rig everything up in the back of the truck with jumper leads, hit the brakes, and see what the actual load on that wire is to get some idea for what size of wire you need. But rather than dig into the cruise control harness or the SMJ, why not just run it to the brake switch itself? It's not that far away and unless the R50 hid it better than the WD21 did, it shouldn't be that hard to get to.

 

Provided you do the splice properly (just say no to suitcase connectors), and the brake controller doesn't burn up and short out, you shouldn't have an issue with the circuit you're tapping into. That said, if I had to choose between no ABS and the cruise control making the engine fight the brakes, I'd take no ABS any day of the week!

 

Yeah cold just means downline of the switch.

 

I'll look again but from what I remember the switch way at the top of the brake pedal would be much harder to get to than the CC box or SMJ. When my brake switch contact bushing rotted way, it took me two hours to replace it because there was no room to get my hands up there. I had to use screwdrivers like chopsticks.

 

I'm basing the CC on the fact I never use the brake to disengage the CC and I'm trusting myself to either use the switch or just throw in the clutch in a panic situation.

 

Obviously I'll be driving much more conservative with a trailer, but from living in Dallas with high speed aggressive drivers and heavy traffic, my ABS usually engages once or twice a year.

 

Sent from my FRD-L04 using Tapatalk

[Slartibartfast]

Ah, makes a lot more sense with a manual--I was assuming automatic. Sorry to hear they buried the switch so well.

[emw]

Hi lots of old posts but nobody ever responds and says if anything actually worked??? does anyone have a really good answer here..Im doin it now...the fuse box brake light switch is always hot..so no good..the red wire coming out of the brake light switch behind the brake pedal is always hot..so no good..the other green wire coming from the brake pedal light switch is not hot... however i spliced into it and it has{ no} power when pedal is pressed??? anyone have a solution??..My next step is to tie into the actual brake light and run a wire all the way back under the dash....i will check today and see if that is always hot..What a nightmare...

Edited October 29, 2020 by emw

[colinnwn]

I always intended to do a full writeup of installing the electric brakes. But after years of working on it, and finally getting it in, just in time for a camping trip, and my Pathfinder dying shortly after, I ran out of mental energy. Tapping into a good brake light line was one of the easier parts of putting in the trailer brakes unfortunately.

 

I thought I addressed what ended up working for me in your PM, and the drawback for you to decide, regarding tapping at the cruise box because it was much easier to access, and have room to do a good tap.

 

I always cut the wire I am tapping, and put in a heat shrink crimp splice, with the extra wire running out of one side of it. I never use those saddle taps you just click over a wire. They're crap. Even if you get what appears to be a good connection, a couple years later they frequently fail due to corrosion, or the tapped wire working itself up slightly from the metal splicing fork. They are extremely sensitive to having the correct gauge wire it is splicing, one gauge too big of a tap they barely connect, one gauge too small they actually reduce the current capacity of the wire it spliced.

 

The service manual might help you if you can read circuit diagrams. It is on EL-68 in the 2001 service manual. I attached a screenshot of that page. 

 

If you spliced into the green/yellow stripe wire at the switch, and tested it for voltage when you pressed the brake pedal, and you had the battery connected, and didn't find any voltage, then you messed up somehow in your test or tap. I've done that kind of thing before like not verifying I had the test meter probe on a good ground. The first thing I'd do is verify that the brake lights are coming on, and then test again. If lights work and still no 12 v, and you used a saddle tap, replace it, or test another way with a tiny wire backprobing the connector for example, and decide if you really want to use a saddle tap.

 

There will never be always hot around the stop lamps. The green/yellow color carries through all the way to the stop lamps and is basically a continuation of the exact same circuit. So tapping in at the stop lights as long as you use the green/yellow and not the black, will definitely work too. But if you can't get the signal at the switch, you are unlikely to find it there.