Troubleshooting Trailer Taillights that Stop Working When Head Lights are Turned On

Question:

I have a 2011 Tahoe and when the trailer is hooked up and you turn the truck lights on the trailer lights go out. Have checked fuses and are fine. When turn the head lights off and note on auto they work.

asked by: Don 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 tail lights 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 tail lights 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 tail lights. 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.

What you described is a textbook ground issue. When the headlights additional amperage is drawn and the weak grounds of the trailer prevent the lights from working.

expert reply by: Jameson C