Troubleshooting Trailer Lighting No Right Turn Signal Unless Brakes are Applied

Question:

I bought utility trailer used. Existing lights corroded. Replaced lights and tested. Problem: No right turn signal unless brakes are applied. All other lights are fine.

asked by: Mike B

Expert Reply:

I would start by using a circuit tester, item # PTW2993 if needed, and checking the connector at the rear of the vehicle. Make sure that the left turn and brake signals, right turn and brake signals and the running lights are working properly. If all is good on the vehicle, then the problem is on the trailer.

The right turn and brake signal are carried on the same wire on the trailer so both brake and turn functions should function unless there is a problem with the wiring or the bulb in the trailer light.

Another possibility is that there is a problem with the ground to the trailer light. Trailer lights are grounded through the mounting studs. Make sure that the connection of the light to its mounting bracket and the bracket to the trailer frame are not corroded or rusted and that paint is not inhibiting the ground connection. If this problem only exists with the running lights on, then it is most likely a faulty ground.

expert reply by: Robert G