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Troubleshooting Wiring on a Trailer with Separate Brake and Turn Signal Lights


I have a 2018 Subaru Forester with a factory installed 4 pin trailer wiring connector. I just built a custom tear trailer and have installed separate turn and stop lights along with a top center third stop light. All lights are LED. I have continuity and power at the ends of all circuits. I tried installing a Tekonsha 118158 converter without success. When I diagram the wiring, I also end up with an extra brown wire for which I cannot find a home. I can send my diagram and perhaps you can show me what I am doing wrong. Thanks


Expert Reply:

There are two things that may help to solve your predicament.

The easier one is the converter. The converter that you used, part # 118158, is not compatible with LED lights. So, even if the wires all lined up where they needed to go, it wouldn't have worked anyway. We don't currently carry a 2-to-3 converter compatible with LEDs.

As for the wiring, that's a little harder to figure out. From what I can tell, you might be using a wishbone 4-way harness on your trailer. These differ from others by providing two brown wires for the tail lights (one right and one left). Try connecting each to their respective tail lights and see if that helps to get everything working.

Your configuration should end up with the 4-way harness's wires like this:
White - grounded
Left Brown - to left tail light
Right Brown - to right tail light
Green and Yellow - to Curt Converter

and the converter wires like this:
Yellow - to left light (for turn signal)
Green - to right light (for turn signal)
Red - to each of the brake lights using jumpers

If that doesn't solve your issue, then let me know and I will try to help further.

expert reply by:
Kef G

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