Troubleshooting Trailer Wiring That Performs Different When Vehicle is In Drive or Reverse

Question:

Good afternoon. Im here in St. Charles and love shopping withe etrailer.com! Heres my problem: Ive got a relatively small trailer carrying two PWCs. Trailer has 1 side running light on each side. Has one tail light on each side, then a band of three rear lights in between the tail lights. The band of rear lights stays on all the time, which is fine. In D the drivers side light and passenger tail light are out, but the rear blinker works. In R it switches, and the passenger side light goes out along with the drivers side tail light, but again the rear blinker works. I just dont even know where to start to try to figure this out, so any suggestions would be very appreciated! Thanks.

asked by: David F

Expert Reply:

First thing you should do at this point is test the 4-way of the wiring harness with a circuit tester part # 3808 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