Troubleshooting Trailer Lights that Dont Work but Tester Works Fine

Updated 06/06/2018 | Published 06/05/2018

Question:

The plug on the wire harness has 3 lights on it. When plugged in all 3 lights are on but none of the lights on the trailer work. Any suggestions.

asked by: Robert

Expert Reply:

It sounds like you're referring to a 4-way trailer connector that has test lights on it like the Hopkins # HM48148 does. And the test lights are working fine but the trailer lights aren't working. There's a few reasons this could be happening.

Since the test lights are on you definitely have power coming from the vehicle connector; however, maybe not enough. The test lights are probably LED which require a lot less power than incandescent lights do. You may not have enough power to the actual trailer lights.

There also could be damage on the trailer's wiring further back than the connector. Or the wires on the backside of the connector are damaged or corroded. You want to inspect the wiring from the connector all the way back to the lights looking for any damged or pinched areas.

Finally, make sure al of the ground connections on the trailer and its lights are made to good, clean, bare metal surfaces. This includes the main ground wire from the connector and any grounds from the lights themselves, if they have their own. If the lights are grounded through the mounting hardware then make sure the hardware and the connection points are all clean as well.

If you still can't find the problem let me know and we'll keep troubleshooting.

expert reply by: Charles S