Troubleshooting Left Rear Trailer Light That Glows with Vehicle Turned Off

Updated 05/27/2024 | Published 04/02/2014

Question:

about 9 months after installation that seemed trouble free, I am finding that the left rear tail lights are glowing when vehicle is off. what gives?

asked by: Bruce T

Expert Reply:

It sounds like there may have been a short on your trailer that caused the converter box of Curt Wiring Harness part # C56330 to short out and now there is a low amount of voltage on your left rear tail light.

We see this problem a lot, and actually the # C56330 did its job and protected your vehicle wiring. They are designed to act like a fuse between your trailer wiring and vehicle wiring so that you do not damage your vehicle wiring.

You can further test the converter box by testing the circuits going into the box by function and then testing the output side as well.

What you will need to do is find the short on your trailer wiring and fix it as necessary and then install a new wiring harness. Look for obvious signs of shorts like cut or exposed wires.

I attached an FAQ on trailer wiring plus an FAQ on troubleshooting 4-way installs.

expert reply by: Jameson C

Joel B.

5/25/2024

I had a short while replacing a bulb with the lights on; it blew the 10 amp main power fuse. When I replaced the fuse with the car lights off, the trailer tail lights came on. It appears the switch box must have burned the relay in the on position. With a main power fuse this should have been protected. This seems like a design flaw. At this point it appears I am stuck having to buy another wiring harness!? Please advise.

Jameson C.

5/27/2024

@JoelB It's super frustrating but the harness technically "did it's job" as odd as that sounds. These are designed to basically self destruct before letting a short get back to the vehicle's wiring. This basically protects the vehicle from getting a short but it does get annoying as it requires replacing the kit if something happens.