How to Convert the Trailer Wiring Harness for a 2007 VW Passat to Tow a Trailer with European Wiring


I installed the T-One harness as per the instructions but I have now a couple of questions: - The VW has amber turn-signals and separate brake lights as it is common in Europe but the plug seems to provide only the typical US signals, i.e. brake lights and turn signal on one bulb. My trailer has amber turn signals and on all my previous vehicles, I just paralleled-outfoot the signals from each light. Is there a way to change the output so I dont have to re-wire my trailer? - What is the proper way to test the outputs on the plug provided? Using a test light, I dont seem to get all the functions. Thanks!


Expert Reply:

The T-One Vehicle Wiring Harness, # 118530, is designed to convert the European wiring on your 2007 Volkswagen Passat to the standard trailer wiring configuration used in the United States. This configuration has 4 wires, one is a ground wire (white), one is a taillight wire (brown), one is the left turn and stop light wire (yellow) and one is the right turn and stop light wire (green). I added a video that shows how to test the wires with a circuit tester like part # 40376, see link.

If your trailer has amber turn signals separate from the stop light circuit, you would be able to add a converter in the trailer wiring to separate the brake and turn signals, as long as there are no more than one incandescent stop and turn signal bulb on each side of the trailer. This conversion is the one option that we have for wiring your trailer with European style wiring because your vehicle requires a powered module to protect the sensitive circuitry and computers in the Passat. The only other option is to change out the lights on your trailer to lights that have combined stop and turn signal lights.

You will need a vehicle to vehicle tail light converter, part # 118158, which will separate the turn signal circuit from the brake light circuit. On the input side of the converter, you will attach the right turn/ brake circuit to the green wire, the left turn/ brake circuit to the yellow wire and the white wire will ground to ground wire from the trailer connector that is grounded to the trailer frame. The running light circuit will bypass the converter entirely, since it does not need to be converted.

On the output side, the yellow wire connects to the lead for the amber turn signal lamp on the drivers side, and the green wire connects to the lead for the amber turn signal lamp on the passenger side. The red wire is spliced to each side of the trailer and connects to the red stoplight lamp wires, and the brown wire that bypassed the converter is spliced to each side of the trailer and connected to the running light lamp wires.

To complete your trailer wiring you will also need a 4-Way trailer side connector, like part # 18004. I attached a drawing that shows how the converter should be wired to the trailer lights.

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expert reply by:
Robert G

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