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Trailer Lights Stopped Working Using Trailer Wiring Harness 118449 on a 2009 Toyota Highlander

Question:

I bought a hitch and wiring harness from you in 2009 for my 2009 Toyota Highlander Hybrid. It apparently worked fine until this June - although I have rarely used it. I bought a new utility trailer - just two tail lights, but great quality. Lights all worked fine when I tested it at purchase and when I left Texas for NY. About halfway to NY, I checked the trailer lights and found that they no longer worked. All lights on the SUV work fine. I checked all the fuses for the trailer lights about six times now both visually and with a tester on the tops of the fuses. All are good. Both under the steering wheel and under the hood. Then I tested the white connector in the left rear quarter panel, where your harness hooks in. That white connector on the car side has no power. What could the problem be? Maybe the portion of your harness that goes near the brake pedal? Can I jump wires off of the tail light harness and bypass the white connector in back? Can that all be done on one side? I am 30 miles from a Toyota dealer and its hard to take it in a leave it, plus $125/hr to diagnose. I found another guy on a blog with the exact same problem with his hybrid toyota, so I assume it is with the car. What can I do?

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Helpful Expert Reply:

The first thing I would check is the small fuse that is part of the converter box wiring for harness # 118449. If that fuse is loose or blown the whole harness will not work. And if it is blown it is possible that a short on the trailer caused it to blow and until that short is found and fixed it would just keep happening.

If the fuse is not blown then the converter box itself could have blown and the harness would not work. You would need to replace the wiring harness. You can also check the vehicle owners manual for any relays related to the tow package wiring and check them.

Check the vehicle and trailer side connectors for dirt and corrosion and clean them. On the trailer, though it is new, make sure there are no broken wires and that all the grounds are attached to clean and corrosion free bare metal surfaces.

You would not want to run wires from the lights on the vehicle because your Highlander requires a converter. The brake lights and turn signals are separate on the vehicle but trailers use a combined brake light and turn signal system. At this point I am willing to bet it is either the converter, its fuse, or a relay that is causing the problem.

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