Trailer Running Lights on 2 Trailer Do Not Work when Connected to 2004 GMC Yukon

Question:

2004 Gmc yukon SLT.Factory trailer hook up on truck with this adapter. Tried two different trailers, same results. Turn signals LF,RT, work ok. Brake lights ok. But with lights on no lights on trailer, Do I need some type of fuse in truck? Thanks for your help.

asked by: Larry G

Expert Reply:

It sounds like there is a ground problem. But first, you will want to test the connector on the truck without the adapter and then with the adapter. Use a circuit tester such as # PTW2992 to test the pins on the truck side connector while someone sits in the truck and goes through the lighting functions.

If the running light circuit does not work then check the tow package fuses using the owners manual to locate any and all of them. A blown fuse could be the issue.

If it checks out fine then plug in the adapter and perform the test again. If it does not work properly then the issue is with the adapter and it will need to be replaced. If it does work properly then it is likely a problem with the trailers.

Make sure that the truck side connector, adapter, and trailer side connector are all clean and free of corrosion inside and out because that, too, could cause this problem.

On the trailer side, make sure the main trailer connector and the grounds for all of the lights are attached to clean and corrosion free bare metal surfaces.

If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H