Trailer Lights Go Out when Headlights are Turned On

Expert Reply:

The first thing we need to do is eliminate the vehicle and its wiring as the cause of the problem. Use a circuit tester and check each pin of the connector while that function is activated (Yellow wire for left turn/ brake, green for right turn/ brake and brown for running lights.) Once you eliminate the vehicle side as being the problem, start at the vehicle/ trailer connection. Is it tight and not corroded? Trace the wiring back from the connector to the trailer. Is the ground (white) wire securely grounded to clean metal on the trailer? Is the wire itself in good condition, with no worn insulation, no broken wires, no corroded connections at the lamps? By following these steps, most wiring problems can be identified and fixed.

expert reply by: Mike