Brake and Signal Lights Do Not Function When Head Lights are On

Question:

brake and signal lites work fine when headlites are off,when headlites are turned on they do not work and also the rear and side marker lites do not work at all.Please advise on how to correct problem

asked by: John C

Expert Reply:

It sounds like you have a bad ground connection. If all ground connections are not making good contact to bare metal, when the taillights are turned on then the trailer lights will go out or not function properly.

You will need to check all of the ground connections especially where the taillights are mounted to the trailer frame, and where the light brackets are mounted if they are bolted to the frame. If a plastic license plate holder is mounted between the left side taillight and the trailer frame this could be the problem.

Once you have all of ground connections checked, if the problem persists, you will need to check for a broken pinched or frayed wire on the trailer somewhere. If this is not the case then you will need to use a circuit tester, item # PTW2993 if needed, and make sure your wire connections have been properly made at the taillights. You should also check the connectors for corrosion that can sometimes cause issues with the trailer lighting. If you look into the connector and see green corrosion you will need to clean out the connector.

expert reply by: Robert G