Troubleshooting Malfunctioning Trailer Left Turn Signal Due to Poor Ground Connection

Question:

hooked up 4 pin lights to expedition. running lights work, right hand signal works left hand work until put head lights on. right signal works . Left wont work emergency blinckers wont work

asked by: George A

Expert Reply:

So everything works as it should, until you turn the headlights on is that correct? If so, what you describe are the symptoms of an insufficient ground connection, likely where the driver's side taillight grounds to the trailer frame. Make sure that ground connection is securely made to clean bare metal on the trailer frame. Trailer lamps will pick up their ground connection either via it's mounting studs being in direct contact with the trailer frame or through a dedicated ground wire connected to the trailer frame. If the connection is slightly loose or has some corrosion, it would certainly cause the problem you mention. While you're at it, it couldn't hurt to check the ground connection on the other taillight and the main ground where the trailer connector grounds to the trailer frame, typically on the trailer tongue. All connections should be tight and free of corrosion.

I'll link you to a help article that will help with your troubleshooting efforts.

expert reply by: Mike L