Trailer Wiring Issue

mllc · May 22, 2011

Hi all,

I have a problem with my truck's trailer wiring, and I was hoping someone could shed some light ( no pun intended) on it. When I connect my trailer to my truck, the right stop light turns on and stays on, even when the truck has been sitting for days. It doesn't do this on other trucks, so I know the trailer is not the problem. Also, when I turn on the left blinker, both trailer lights flash. I took a multi-meter to the harness plug (the part that connects into the 7-way plug on the tow hitch) and the truck is sending 11.5 volts to the right trailer light all the time, and the same holds true for when the left turn signal is on. The wires all appear to be in excellent shape and I can find no eveidence of broken or coroded wires. anyone have any ideas? I'm making an apointment tomorrow for the truck to be looked at by the dealer but I'd like to fix this myself.

Thanks Guys!

markw8 · May 23, 2011

Did you take the plug apart and inspect it? Both ends? Also be sure of the integrity of the ground thru the plug and to the trailer frame.

Mark

mllc · May 23, 2011

Did you take the plug apart and inspect it? Both ends? Also be sure of the integrity of the ground thru the plug and to the trailer frame.

Mark

I did take it all apart and it looked new, I even took the plug from my dad's gmc and tried it on mine and it did the same thing. I tested the ground and that's fine too. I just ordered a flasher relay from rockauto, I was reading some posts with people having similar issues and that's what it was, I'll wait for it to come in before I call the dealer

dragland · May 23, 2011

I know you said you checked the ground, but look harder. Thats the problem. I never ground trailer tail lights to the trailer frame, I always run a seperate ground wire to the plug. That avoids any problems. I'd say you have a light that is not grounding and backfeeding throught the system.

Good luck, these things can and will drive you mad.

mllc · May 25, 2011

Update: the new relay came in, Once I installed it, the trailer behaved as it should, however, the relay they sent me was the wrong part number,so the turn signals on both truck and trailer were flashing like crazy. I sent the old one back and as soon as they credit my account I'll be ordering the correct one to match the part number I had in the truck.