Troubleshooting Trailer Wiring When Left Turn Signal And Brake Light Does Not Work

Question:

Running lights Work,But Left side brake and signal trailer lights not working. Ive already replaced left trailer relay.

asked by: David G

Expert Reply:

It sounds like there may be a ground issue on your trailer. A weak ground may cause problems like you describe and can be intermittent. You can use a circuit tester like part # PTW2993 and test the vehicle connector to make sure all functions are working.

You will want to visually check the wiring on your trailer to make sure there is no sign of corrosion or damage to the harness. make sure the harness ground is securely attached to a clean bare metal surface.

Then check the wiring on the trailer for any signs of loose or damaged wiring and correct. Check each of the light assemblies and make sure they are all grounded to the trailer as well.

expert reply by: Jeffrey L