Why Are My Trailer Taillights Staying On when Using the Curt Harness # C55378?

Published 05/06/2022

Question:

I have a 2001 tundra, i purchased a CURT 55378 installed. For some reason the lights on My trailer , left and right stay on all the time, right side brighter than the left, even when the truck is off. I have to disconnect the pin so the lights turn off. I used a circuit tester both right and left green lights turn on and stay on. Nothing else works, not the brake, or turn signals. Do I have to replace the harness?

asked by: Amador T

Expert Reply:

If you have tested the Curt Harness # C55378 with a circuit tester on your 2001 Toyota Tundra, there should not be any signal to the plug when the vehicle has the lights off and there should be power to the lights when the vehicle is turned on. If you tested and there is a signal with the lights off, there is a problem with the vehicle's-side of the connection.

To rule out any issues with the vehicle's-side of the wiring, make sure that there are no frayed/pinched wiring and that the ground wires are connected to a bare metal surface.

The other possibility is an issue with the converter box on the harness itself. In order to check for a converter issue, the need to test the wiring going into the box for functionality. If the functions are incorrect going in, you need to re-wire the harness "from scratch" as if you are wiring it up for the first time. I went ahead and attached a video that walks you through this process.

If, however, the functions of the wires are correct going into the converter but incorrect going out, then this is a tell-tale sign that you need a new converter. If the signals are correct on the input and output of the box, the issue lies elsewhere.

As far as a replacement box, I strongly recommend going with the Tekonsha T-Connector # 118378 over the Curt harness you have. The Tekonsha harness has a much higher-quality converter box than all of the other harness models we carry.

expert reply by: Bob C