Trailer Lights Malfunctioning when Connected to Old Truck but not on New SUV

Question:

If I run a ground wire white from the light mounting stud all the way to the trailer to car flat 4 connector, does the trailer ground wire white also have to ground to the trailer frame? Issue with both trailer turn signals flashing when one is turned on. When connected to an old Toyota pick up truck. No issues when connected to new Hyundia SUV.

asked by: Jim

Expert Reply:

If you are having issues with the lights on your truck but not with a newer vehicle, then the grounding issue is due to the grounding wire not making a clean enough contact to the truck's frame. Old trucks have plenty of rust and corrosion that prevent a proper contact.

You can sand down an area of the frame to ensure a good connection and then apply dialectic grease, part # 11755, to ensure this connection doesn't succumb to rust or corrosion in the future. I've linked to a video review of this grease for you to look at.

If the problem still persists after that, then test the connector on the truck with a circuit tester, part # PTW2993, to see if you are getting power at both turn and brake signals. If not, there may be a problem with one of those wires. You'll need to trace those wires and look for any frays or contact with the frame or other wires.

expert reply by: Kef G