Troubleshooting Trailer Wiring Where Both Turn Signals Blink With Brakes On

Question:

Truck lights work fine trailer wires when running lights are on or brake is pressed with turn signals on booth blink

asked by: Wayne W

Expert Reply:

First thing you should do at this point is test the 4-way of the wiring harness with a circuit tester part # PTW2993 for voltage on all of the right pins when the taillight signals are being applied. Just like in the video I attached.

If the voltage checks out there but the trailer lights still don't function right then the problem is on the trailer wiring. That would mean that problem is either due to a ground issue or a short issue.

Make sure that the trailer side connector are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and corrosion free bare metal surfaces.

I suspect that on either the truck side or the trailer side there are circuits that are shorting out together.

I attached a help article on trailer wiring for you to check out as well.

expert reply by: Jameson C