I have a 7 pin flat connection for truck and horse trailer. Bought a vehicle side plug-in LED tester. Tail, turns, and brake lights seem OK. Nothing on trailer works. I suspect ground connection on trailer. What is best way to confirm this? Note that all except left turn and left brake worked OK thru 3 hrs of towing, then I went to park the trailer and nothing worked. I checked vehicle after that happened and rechecked today and it seems fine. Ground on trailer is not easily accessible so what is best way to pinpoint problem? Thanks.
Expert Reply:
When intermittent lighting problems like you describe occur, it is almost certainly a ground problem. The ground connection on the trailer is not up to the task, when the lights DO work, you are probably getting ground through the trailer ball.
The main places to check are the point where the ground wire coming off the trailer connector attaches and the attachment points for the light fixtures. If any of these attachment points are loose or are corroded, your lights will not work correctly.
If the attachment point for the ground wire from the trailer connector is inaccessible, you can create a new grounding point in an area that is easier to reach, like the trailer tongue closer to the coupler.
expert reply by: Mike L
