Trailer Lights Do Not Work After Installing Wiring Harness 118379 on a 1999 Toyota Tacoma


I plugged everything in, all truck lights work fine but I get no lights on my trailer when I plug in .


Expert Reply:

There could possibly be a bad ground. First, check the white ground wire on the converter box for # 118379. It should be attached to a clean and corrosion free bare metal surface. Then use a circuit tester like # 40376 if needed to test the wires going into the converter box from the truck. If the signals are correct going in then test the pins on the 4-Way. If the signals are not coming through then that indicates a bad converter box and it will need to be replaced.

If the signals are not correct going into the box then there is an issue with the connection points on the truck or the truck wiring. But since your truck lights are working I do not think this is the case.

If everything checks out ok on the harness then the issue must be on the trailer. First check for dirty or corroded pins on the 4-Way, trailer side and clean them out. Then make sure the main trailer ground is attach to a clean and corrosion free bare metal surface and do the same for the lights.

If the trailer has a lot of lights that draw more than 2.1 amps per side for brake lights/turn signals, and/or more than 4.2 amps total for running lights it will be too much draw for the converter.

expert reply by:
Michael H

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