Troubleshooting Trailer Wiring Harness Working Intermittently on a 2015 Ford Escape

Question:

I am not getting the brake lights to work when I test them. Does the car need to be in Drive or in motion for the trailer brake lights to work? SHould there be voltage with the brakes applied and the vehicle in Park? The first time it was installed their were no parking lights, now I have parking lights and no brakes. Any help is appreciated. Thanks,

asked by: Steve

Expert Reply:

Basically any time the vehicle's brake lights or parking lights would illuminate the trailer wiring circuits on the 4-way would do the same.

Based on how at first only the parking lights didn't work and now the stoplights don't work either that would lead me to believe that the problem is a loose connection. Since you didn't say if you tested this with a trailer connected or with a circuit tester at the vehicle 4-way first I would test the 4-way on the vehicle.

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. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

If the problem is on the vehicle side then I would first recommend you double check how the harness is installed on your vehicle, make sure all of the connections are good and tight. You should check all towing related fuses and relays as well.

expert reply by: Jameson C