Troubleshooting Trailer Wiring with Lights Not Working Completely

Question:

i have a problem with a 7 pin hookup. when i plug the trailer lights up only partly the running lights work, the driver side turn works, and both brake lights work. the passenger turn doesnt work and the other lights only work when the plug is only partly plugged. if fully plugged none of the lights work. also when partly plugged in the running lights on the truck get brighter. i have checked the wires on both truck and trailer, and both have no showing wires and as far i can tell they are both wired correctly. i have checked the ground on both and cleaned both to make sure the are properly grounding. but still having problems

asked by: Michael

Expert Reply:

I think I can help but it still sounds like a ground connection issue. Here is why...whenever some functions work and others do not, it is either a connector issue, a short in the wire, or a weak ground. Since everything works on both the trailer and truck when tested independently, and when you partially plug in the system it seems to work better than fully plugged, it definitely sounds like a ground issue. Since you have already cleaned up your grounds, I recommend moving them. Make sure you have bare metal to metal contact for both the vehicle side of your 7-way and the trailer side. Then also make sure the ground connections at each light are also bare metal to metal. I'm guessing that is why the turn signal on the passenger side isn't working when the brake light does.

Finally, use sand paper or steel wool to clean the 7-way connectors on both sides and then use dielectric grease # 11755 to keep moisture and debris out.

expert reply by: Jason S