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Trailer Brake Lights not working

No brake lights on trailer - Running lights, turn signals, and flashers work

Trailer Brake Lights not working

Postby MileHighJC [OP] » Mar 02 2015, 7:20pm

Here is my situation.

New to me 2000 Silverado 2500. I purchased to tow my boat. All trailer lights worked correctly when towed with a friends truck last fall.

Went to test the lights to the trailer yesterday, and everything works except the trailer brake lights. Running lights work, turn signals work, flashers work. Brake lights do not.

Everything works correctly on the truck (all three brake lights).

I have checked every fuse up front that was labeled TRL. All have continuity.

I checked at the stock 7 pin, when running the turn signals, I see voltage on both pin 5 and 6 (yellow wire and green wire respectively), but nothing when I put on the brakes. Im trying to trace backwards, but dont know where I should check next (other end).

Any suggestions appreciated...

Thanks in advance!

Jeff
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Re: Trailer Brake Lights not working

Postby MileHighJC [OP] » Mar 02 2015, 10:55pm

Update, not sure if this will help narrow down at all.

Disassembled the 7 pin connector, cleaned the contacts, reassembled, no change (wasnt really expecting one, but wanted to eliminate that). However I did notice something odd... flashers work if the running lights are off, they do NOT work if the running lights are on.

When I bought the truck, they replaced the multifunction switch to resolve a problem with the turn signal lights coming on when the brake was pressed...

I HATE electrical problems. May just take it back to them and let them shoot the bug.
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Re: Trailer Brake Lights not working

Postby bmerr98 » Mar 03 2015, 3:42am

Regular light bulbs or LEDs on the trailer? If regular bulbs, give them a wiggle and see if that helps. Sometimes it's the simple things that we overlook. I've learned about the bulbs a few times...
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Re: Trailer Brake Lights not working

Postby ASTE25 » Mar 03 2015, 4:39am

Check the trailer light fuses in the under hood fuse box.
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Re: Trailer Brake Lights not working

Postby MileHighJC [OP] » Mar 03 2015, 4:46am

Thanks guys... Lights on the trailer are standard, but all work when hooked up to friends F150. I had checked the fuses earlier today, they are all good. Im suspecting the multifunction switch on the column. It was replaced by the dealer before I bought the truck because of an electrical fault between the brakes and the signals. I had been assuming that it was good (since it is new), but it seems all my research is pointing there.
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Re: Trailer Brake Lights not working

Postby scottl » Mar 03 2015, 6:26pm

First thing to check when diagnosing trailer light problems.Is the grounds.Make sure you trailer is grounding to truck good thru the ball first.Then check trailer grounds then truck grounds.
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Re: Trailer Brake Lights not working

Postby MileHighJC [OP] » Mar 05 2015, 12:44am

Grounding is good... I know trailer works with another truck, but I also broke out the meter to check the truck. Im very suspicious it is the multifunction switch that the dealer installed to fix a turn signal issue. I actually found a stray white wire on the harness that was not connected. I didnt get a wiring diagram before I took it to the dealer, but if it is not resolved when I get it back, that looks to be my next step. Truck is at the dealer now, hopefully get it back tonight (fixed I hope).
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Re: Trailer Brake Lights not working

Postby MileHighJC [OP] » Mar 24 2015, 7:08pm

Update:

The dealer I bought the truck from is still working the problem. In total, the truck has been in 4 times now. Before I purchased the truck, they replaced the multifunction switch (to resolve a short between the brake and turn signal). I then found the problem with the trailer brake lights, and took it back. On the way I also found that the left turn signal would cancel the cruise control. They said the found a problem with one of the wires, but when I picked it up, it still wasnt right. I took it back to them, and when I picked it up they said it was resolved... not so much, when I got home, I found the left turn signals on the trailer didnt work (truck was fine). Got the service manager involved. The next time, they came down to pick the truck up, and delivered it back to me after it was "fixed" (they replaced the 7 pin connector). The service manager told me that he personally had tested it before the truck left their service dept... and that they had replaced a fuse. But, by the time I tested it at home, it was not working again - but now the problems are intermittent. First the turn signals didnt work, now they do, but the brake lights dont work.

They picked it up again yesterday, and will deliver it back to me when resolved... Speculation is that there is a connection that is not solid somewhere that it intermittently causing a problem after the truck has been driven (bumped around).

The bad news is that it has been in the service bay 4 times for what should be a simple problem. The good news is that they have been great about "doing the right thing".... I like the service manager a lot, a no excuses straight shooter. Initially I thought the techs were incompetent, but now I think they are chasing an intermittent ghost... hard kind of problem.
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Re: Trailer Brake Lights not working

Postby esox07 » Mar 25 2015, 3:12am

The problem is a pain but at least the dealer is doing you right
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If you can't fix it with a hammer, it is an electrical problem
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Re: Trailer Brake Lights not working

Postby MileHighJC [OP] » Mar 26 2015, 3:27pm

This dealer is going to have earned my business for a while. Service Manager called yesterday, by the time the truck got to them, it was working again, but he has seen the problem himself, so is not pushing back on me. They have worked on the ground, and were going to test it there this morning, then he is bringing it down to test on MY trailer... Have to say they are doing everything I could ask for.
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