Only Right Turn/Brake Lights Work After Installing Trailer Wiring Harness on a 2003 Toyota Sequoia

Question:

I installed a 20137 wiring harness and the only lights that work on the trailer are the right brake light and the right turn signal. No running lights and no left brake or turn signal. Did I do something wrong? The harness matched the existing plugs perfectly and pluged right in. Thank you

asked by: Dan W

Expert Reply:

In order for the trailer connector # 20137 to work, your 2003 Toyota Sequoia would need to have been equipped with a factory 7-Way trailer connector. If it never had a factory 7-Way, even though the connection points are there, the harness will not be fully functional. You may be able to take the vehicle to a dealer to have the missing components installed to make it fully functional. Also, it is possible that some relays or fuses would need to be installed in order for the connector to function.

If you do have the factory tow package, then there could be a problem on the trailer side. Use a circuit tester like # PTW2993 if needed to test the pins on the 7-Way with no trailer connected. If there is power at the pins but not the trailer, that indicates a problem, most likely a bad ground, on the trailer.

Make sure the main ground from the trailer connector and all of the trailer light grounds are attached to clean and corrosion free bare metal surfaces. Also check the trailer connectors for corrosion at the pins and behind them where the wires attach.

expert reply by: Michael H