Trailer Brake Lights Do Not Work Could the Vehicle Ground Be the Culprit

Question:

All the lights on the trialer work,with the exception of the brakes. i believe its a ground problem, however I tried to run a wire direct from Negative cable and that did not work either. So I am stumped, any other ideas? Could my ground on the Vehicle be a problem?

asked by: Paco

Expert Reply:

Yes, the ground on the vehicle could be an issue. If you start by checking the trailer connector at the back of the vehicle with a circuit tester, item # PTW2993, (no trailer connected) and connecting the ground to the ground post in the connector you will be able to determine if the vehicle ground is the issue. If the brake lights do not work on the vehicle connector when the connectors ground is used, try grounding the tester directly to the vehicle frame. If grounding to the frame works, then the ground wire going into the trailer connector needs to be grounded to the trailer frame.

If you find that the vehicle connector is working properly then the problem is on the trailer. Start at the coupler and check the ground connection there. Make sure it is connected to a clean, paint, rust and corrosion free part of the frame. Next check the taillight brackets and make sure they are connected to a clean, paint, rust and corrosion free part of the trailer frame. Next, make sure the lights themselves are grounded securely and that there is not a plastic license plate frame causing the light on the driver's side to have a poor ground connection.

Finally, if none of the above suggestions work out check along the trailer wiring for a broken, pinched or frayed green or yellow wire.

expert reply by: Robert G