Diagnosing Malfunctioning Lamps on Trailer Towed by 2008 Toyota Highlander

Question:

plug into different vehicle trailor lights work fine , checked plug on highlander and everything works through tester

asked by: Mike

Expert Reply:

Since you have tested the trailer with a different vehicle, and everything seemed to work okay, it would seem that you have ruled out the trailer as being the problem.

You have tested the trailer connector, and have found that each pin on the connector is showing power when its function is activated, which would usually rule out the vehicle.

I would first suspect the ground connection for the trailer connector on the Highlander. Trace the white wire and locate the point where it grounds to the vehicle frame. Make sure this connection tightly made to clean metal. If the connection is corroded, try relocating the ground connection. Having the connector directly grounded to the vehicle frame typically works best.

Closely examine the trailer connector on the vehicle. If it is damaged in some way, you might get a good reading with a tester, but the pins might not match up with the connector on the trailer if something is damaged.

Even though the trailer worked okay when plugged into a different vehicle, you might still take a few minutes to examine the wiring on the trailer. Make sure there are no broken, pinched or frayed wires. Check for worn or cracked wire insulation. Make sure the ground wire from the trailer connector is securely grounded to the trailer frame, and that each lamp is properly grounded either by its mounting studs or ground wire being in direct contact with the trailer frame.

I have linked you to our trailer wiring FAQ article that you might find helpful.

Please let me know what you find.