Troubleshooting a T-One Vehicle Wiring Harness # 118412 Installed on a 2010 Rav 4

Question:

I have a 2010 Rav 4 and purchased your wiring kit last year. Installed it after watching the video with no problems and last year all was fine. This year for the first time I hooked up the trailer and plugged in the connector and noticed an issue involving the trailers passenger side tail light/directional. There is no power to the vehicle side connector for the trailers pass side light until I apply the brakes. Then the brake light stays on, no directional function on right side and light will not go out even with keys out of the ignition until I pull the inline fuse out and reinstall it. I have rechecked all the wiring and found no short. The vehicles lights all function properly, is it possible the modulized box went bad? Is there a way to check it? Totally frustrated. Getting ready to leave on a trip. Please respond as soon as possible. Thank you.

asked by: Robert O

Expert Reply:

The first thing to check is always the ground wire, if the ground is bad you can see all sorts of strange behaviors on the trailer lights.

You will also want to check the grounds on the trailer wiring also just to rule out the trailer causing the problems.

The best way to test the box would be to get a circuit tester like the part # 3808 and test the wires going into the box and then out the other side.

I would start on the left blinker signal wire on the input side of the box. You will want to test for intermittent voltage on this wire, and then again on the output side of the box. If you find that the input wire has the correct intermittent voltage but then the output side has the constant signal that you described then it sounds like the problem is in the box.

If the voltage looks good coming in and out of the box then the next thing you will want to check is the 4-way connector for correct voltage at the right times. If that checks out you will just need to follow the wiring all the way back to the trailer taillights looking for loose wiring or corrosion and fix as necessary.

I attached an FAQ article on trailer wiring for you to check out also.

expert reply by: Jameson C