Troubleshooting 4-Pole Trailer Wiring Harness C59236 Installation in 2009 Audi A4 Sedan

Updated 07/25/2018 | Published 07/23/2018

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Question:

I ordered a Curt trailer wiring harness for my 2004 Audi A5from you, I installed it the exact way I was instructed to, the issue I have is when I use my right blinker, the right trailer signal flashes, but when I use my left turn signal, the right trailer signal flashes for that also. I hooked my car up to multiple trailers so the trailer isn’t the issue. What could be causing this?

asked by: Nicholas B

Expert Reply:

The Curt harness # C59236 you purchased is the correct one for the 2009 Audi A4 sedan and the odd behavior from the trailer lights, like the turn signals activating on the opposite side, is most often caused by an insufficient ground. This usually has a very simple fix.

Remove the ground wire ring terminal and apply sandpaper to that point to remove any paint, primer, undercoat (or rust) that could be blocking the clean ground connection. An application of dielectric grease like # 11755 can help protect that new clean ground connection.

In the unlikely event that this does not correct the issue you can always run a ground jumper wire from the harness directly to the battery ground terminal. Use a butt connector like # DW05745-5 to splice 10-gauge wire like # 10-1-1 (sold by the foot) to the white ground wire and route it up to the engine compartment and to the battery.

expert reply by: Adam R