How to Determine if a Trailer Light Wiring Issue is Originating on the Truck or the Trailer

Question:

For some reason I am having an issue with part of my trailer lights not working. Its the turn signal on the right side of the truck. Ive had a trailer company look at it but they think it is something to do with the wiring on the truck. Any help would be greatly appreciated.

asked by: Mike H

Expert Reply:

If the light issue is on the trailer's right-side, I can help you determine if the wiring issue is originating on your vehicle or on your trailer. If the lighting issue is only on the truck, and not effecting the trailer at all, I agree it sounds like the issue is on the truck.

Using a circuit tester, like # PTW2993, test the vehicle-side trailer connector for each function. This is usually easiest if you can have a buddy inside the vehicle to activate the different light functions while you test for the functions at the connector. I've attached a video showing how to test a 4-Way connector for the proper functions for you.

If your vehicle-side connector tests correctly for all of the functions, we know the wiring issue is on the trailer. If you can provide me with some more information as to what the issue is with the right-side turn signal, what does or does not happen when the signal is activated, I will be happy to help provide further troubleshooting steps.

expert reply by: Victoria B