Troubleshooting a Trailer with No Power in the Harness

Question:

Hooked up trailer to truck but now power on 7-way or 4- way. Is there a relay or fuse that I’m missing it seems all fuses that say trailer are ok. Need help if you have had any customers with this problem. Thanks

asked by: Ruben M

Expert Reply:

The first thing you need to do is to test your vehicle's harness with a circuit tester like part # PTW2993 to ensure all of the functions are working properly. I've linked to a video that can demonstrate how to do this. I've also linked to a help article that can show you the different functions for 7-ways.

If the functions are not testing positively, trace the wires and look for any pinch points, corrosion, or areas that may be exposed. If you find any, replace those wires. It could also still be a bad fuse or relay. Carefully inspect all fuses and relays and replace those that are blown. There is a high possibility that this is where the problem is.

If everything is working properly, the problem is on the trailer side. Ensure that the ground wire (the white one) is connected to a paint-free, clean metal part of the frame. Any corrosion, rust, or paint between this connection will cause you to lose functionality.

If that is looking alright, then trace those wires like above and look for the same things.

If you see no problems there, you may need to replace your trailer's wiring harness.

expert reply by: Kef G