Troubleshooting Running Lights on Enclosed Trailer Towed by 1997 Ford F-350

Question:

I have a 1997 F350 7.3 and A 7x16foot enclosed trailer. I went to fix the connections on the trailer side, reconnected the wires together and I still dont have running lights. I checked the fuse in the truck and thats still good. What else can it be?

asked by: Matt

Expert Reply:

The most common reason why trailer running lights won't work is a bad ground. The ground problem could be on the truck's wiring harness, the trailer's wiring harness or both. The good news is that it is easy to check your grounds.

Trace the white ground wires on your truck and trailer harnesses to the spots where these attach to the frames. The best fix is usually to remove those ring terminals and sand off those grounding points to expose clean bare metal. An application of dielectric grease # 11755 will help protect that new clean ground connection.

You can also inspect the running light contact on both the vehicle socket and the trailer plug to ensure that there is no corrosion, dirt or trapped foreign material in that connection that could be clocking the running light signal. The linked photo shows you which pin on the 7-way socket carries the running light signals.

expert reply by: Adam R