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Discussion Starter #1
Ok, on my 01 my trailer brake-lights don't work. I have turn signals, hazards, park lights, and trailer brakes on the trailer, the only thing that doesn't work are the stop lights. They don't work from the factory 7 pin plug or my 6 pin plug up in the box. I have checked every fuse under the hood and the ones in the cab with a test light and they're all ok. I went over the wiring from in firewall to tailgate with no luck. I'm stumped.


Is there some kind of relay to make the switch from seperate signals on the truck to the stop, turn, tail on the trailer? If so where is it? Edited by: Diesels Forever
 

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I had a similar problem on my 2000 Z71. Check your plug on the truck and look for a bent pin that is not making contact. That is what happened to me. Striaghtened the pin with a screwdriver all was fin. It is a shot in the dark, but worth a try.





Bill
 

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Did you check the iside of the Female plug on your trailer wiring???



There might be some corrosion in there , cleanit with a shot of either.


Just my 2 cents.



Cosgrove
 

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Ok you should have the 7wire round plug on your bumper. Look under the rear of the bed and there is a pigtail wire harness that will plug into the main truck lights. There is a yellow or blue wire that will come out of that harness and down to the trailer plug. You need to check that wire. Sometimes it will come loose and you will need to fix the prong end of it. Try that and see what happens.
 

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Did you check to make sure you have brake lights on the truck? Your truck has seperate turn signals and brake lights which is different from most. If you have brake lights on the truck and not on the trailer it sounds like there is something wrong with the converter that combines the t/s and brake lights. I've never looked into what is actually used to do this but I can if you suspect that is the problem. I assume there is some kind of converter.
 

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on the new trucks there is a relay you have to get to make brake and turn signal back to one wire if you have the amber turn signals in back you need the relay, red turn signals brake and turn are same wire
 

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Well after reading Turfmower's post, I went out and checked mine. I needed to get the bed plug installed anyway. I didn't have to install anything extra over the additional plug in the bed and my truck came with both the camper and trailer packages from the factory.


My test light says the brake lights will work okay, power to each of the labled turn signal/stop lights on the Pollack plug.


So I'm really confused about what might be causing your problem if it's not a broken wire someplace. There has to be some way to tie the amber truck turn signals to the brake circuit of the plug, but I don't know how it's done or where. Sorry...
 

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I also read your post about no Brake lights, so I went and checked mine and all is ok. While I was there I took the trailer out for a ride. DAM !!!!!! Can't wait to take that sucker out on the HWY.
 

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This may be a long shot, but have you checked the fuses in the fuse box under the hood? I pulled a friends trailer that must have had a grounding problem and it kept blowing a fuse in that box and I wouldn't have any trailer lights.
 

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Discussion Starter #11



All, and I mean all, fuses are good. I've double and triple checked them. It is not a trailer plug problem, unless all three of my trailers all of a sudden have a bad plug. My brake lights work fine on my truck. I'm going to check the pigtail that GMC2500HD talked about tonight and see if I have any luck with that. I did have a bad wire for the park lights under the bumper, but I repaired it.


I was looking for some sort of relay or pigtail while I was under it fixing the park light wire but it seemed that every wire was pluged into another harness somewhere. I got sort of confused looking at the harnesses for too long, it seemed they were pluging in to each other. I needed a break so I came and posted this thread.


I'll post an answer if I ever figure it out.
 

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Discussion Starter #12
It's gotta be a bad wire under the box somewhere. I was under there for about 20 min jacking around, chasing wires. I never found a bad one but I must have wiggled something right cause the trailer brake lights started working again. Guess it's fixed till it screws up again.
 

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Man i was hoping you found the problem. I have gone though the exact same thing with my truck. Dealer says everthing working fine. But i don't have brake lights.!!! maybe i can borrow your magic wand?
 

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On my dually, and on all the cab chassis I see, there is a junction box of some sort. 4 harnesses (with small pins) plug into it. I believe they are color coded to correspond to what spot on the junction box each plugs into. The blue comes from the front of truck, and also has a lead which goes to the 7 prong trailer plug. Black and Grey go out to left and right signals and neutral(white) is for license/marker lights. Not sure if I'm making much sense, If you've already checked here, or even if the 2500s have this junction box, but I'll try and get a pic at work tomorrow. Look for a bent pin,(pins are in the junction box) broken (or semi broken) wire in this area. Possibly Junction box itself is bad? Box is located on rear crossmember (driver side). A pic will describe what I'm talking about much better. Edited by: skidsteerloader
 
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