Trailer Running Lights Not Working with 2003 GMC Yukon

Expert Reply:

The first step would be to determine if the problem is on the trailer or in the vehicle wiring. Use a Circuit Tester such as the one we offer, part # 40376 and check the running light pin on the trailer connector. If you get a signal on the connector with the headlights on, then the problem is on your trailer. If you do not get a signal, check the auxiliary fuse box under the hood. Your owners manual will show which particular fuse governs the trailer running light circuit. If the vehicle side checks out alright, you will need to check the trailer connector for corrosion or damage. Also trace the wire for the running light (usually the brown wire) back from the connector on the trailer, looking for broken or pinched wires and cracked or worn insulation that would allow the copper conductor to contact the trailer frame.

expert reply by: Mike L