Running Lights do not Work on Trailers Behind a 2005 GMC Sierra Z71

Question:

I have a 2005 gmc sierra z71 and the running lights on any trailer that I pull do not work. At one point they would come on intermidently, Now not at all. Where do I look first and last.

asked by: John

Expert Reply:

The first thing to check is the trailer connector on the truck. Use a circuit tester, like part # PTW2993, clip it to the truck frame, and test the pin for the running lights. I would bet that you will not get anything since you have tried multiple trailers. The next thing to check while you are at the rear bumper is the ground for the trailer connector. Make sure it has a good, clean connection to the truck frame. This is the most likely culprit.

If everything checks out so far, head to the fuse blocks in the engine bay and cab. Try and locate the fuses and relays that have to do with light circuits or towing circuits. Make sure that the fuses are not blown, or the relays are not burned up. You can check the vehicle owner's manual, or the fuse block covers for fuse location and identification.

If you do not find the problem here, the last thing to check is the wiring that runs from the truck trailer connector back. Trace it up as far as you can and look for nicks or fraying.

Write back and let me know what you find. If the problem is not solved, we can start looking at other solutions.

expert reply by: Patrick B