trail brake lites truns signals not working no 04 gmc sierra?

[skip]

i put new fuse box from gm that has new fuses and relays still nothing working i have traced the wiring hardens can not find anything wrong please help me find my problem
and the parking lites work fine

 

[walter chaos]

go back to the auto supply and get a test lite --- disconnect the trailer harness wiring and check all functions of the lights, brake and running lites to see that there is no problem ( you can do this at the Plug to the trailer with the test lite clipped to the bumper and the probe inserted into the plug that is on the car side of the check== trailer checks are only done after it is determined that the wires are ok on the truck side -- with the trailer on the back of the truck and the lite UN-plugged,, get a hot wire from the battery to the rear of the truck __ ground the trailer to the car and check that all th lites work on the trailer and this is with the hot wire and the ground circuit completed by the trailer connected to the truck __ a greasy trailer ball and no ground wire to the trailer will noT close the ground circuit __ if all this checking is preformed in the above steps ( even if you did this already try it AGAIN ) then the source of your problem it the plug-in harness at the rear of your truck .. I had a plug-in for a Jeep that was no good and took it back to the auto store and got another and it was fine for years.....

 

[knuckleheaf27]

in my experience if trailor light arent working right its always the wireing on the trailor