Troubleshooting a Tow Ready Wiring Harness on a 2011 Toyota RAV4 Limited

Question:

I did the install of the T-One #118412 wiring harness for my 2011 Toyota RAV4 Limited so I could rent a trailer. I went to them to get a towing inspection and was experiencing some strange issues. When I connected the trailer to the harness, only the small lights around near the edge of the trailer was lighting up and the main brake/turn signal lights were not. When I hit the turn signal, the small lights would all flash like hazard lights, but nothing would come on on the main lights. When the workers at U-Haul were testing the harness with a tool, everything seemed to be working fine. Their diagnosis was that it was a bad box and wasnfoott putting out enough power to light up the main trailer lights and recommended that I get it replaced. Could this be the issue or is it something else? Thanks.

asked by: Mark

Expert Reply:

It sounds like there is a ground issue on the trailer. Typically, when there is erratic taillight behavior it is because something is not grounded correctly on the trailer. Especially since the guys at the trailer rental place tested the 4-way and said it was working correctly.

To rule this out you could try hooking the 4-way of your 2011 Toyota RAV4 to a different trailer and see if the problem persists. If the problem goes away, you know that it was the trailer and the Tow Ready Custom Fit Vehicle Wiring # 118412 is not at fault.

To test the box, you will need to use a Circuit Tester Kit # PTW2993 and test for voltage going in to box when the different taillight functions are being applied, and then test the output side of the box for voltage also. If there is voltage going in, but none coming out then the box is at fault.

I would also check the ground wire for corrosion, or not being secured and fix as necessary.

I attached an FAQ article on trailer wiring for you to check out, as well as installation instructions and an installation video for the # 118412