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Towbar Electrical: Possible to combine dedicated wiring harness and bypass relay, or?

MarkJ Jul 23, 2013

  1. MarkJ

    MarkJ New Member

    Help please! This has been an expensive year long saga. Thanks in advance for any assistance.


    2008 A4 B7 Avant

    I purchased and properly installed the dedicated wiring harness (Audi A4 Avant 7 Pin Electrics Dedicated Oct 04-08 19010506RC) for my removable towbar about a year ago. The code was entered into the computer and everything should work fine...but, it doesn't.

    1. The brake lights on the trailer do not come on when the brakes are pressed.
    2. The turn indicator lights on the trailer are sporadic, blinking once every 2-3 seconds or twice and then nothing for 3-4 seconds.
    3. The running lights on the trailer all work perfectly. However, there is a warning light about a trailer light being out on the driver's display when the trailer is attached.
    After taking both the car and trailer to my aftermarket Audi shop for full diagnostics, and several emails with tech support, PFJones/Westfalia now says the wiring harness does not work with N. American models. No reason was supplied or, I assume, known. PFJones was helpful in refunding my money and the air freight for the dedicated wiring harness, and sent me a TitanTowbar 7-wire bypass unit.

    I would prefer to leverage the car's built-in towing capabilities (trailer-connected sensing, Trailer-Stabilization-Program, etc.) which is why I did so much research and had everything flown over from the EU to begin with.

    Here are my questions:
    1. Has anyone run into these issues before and found a solution just using the dedicated wiring harness with N. American A4 B7 models?
    2. As the issues are really just 1) turn indicators to work properly on the trailer and, 2) the brake lights to respond on the trailer, could I just run leads directly from the car's break lights & turn indicators directly to the correct pins on the trailer plug (leaving everything else as is, no bypass relay installed)? Is there danger of short circuit or overload of power?
    3. If I have to use the bypass relay, can I only connect power/earth/R&L turn indicators/break lights AND keep the dedicated wiring harness in place so the car goes into tow mode when the trailer is attached?
    Last edited: Jul 23, 2013
  2. MarkJ

    MarkJ New Member

  3. rkanok

    rkanok New Member

    So I have been trying to do this same thing, here is what I found out. the westfalia unit uses the trailer fog light to detect the trailer.

    If you look at the FAQs on their site, it discusses module hum and mentions that the fog light is required.

    I have been trying to decide the best way to fake out the system, I have considered buying an adapter at eurohitch.com but I doubt they handled this so I have also considered making my own with a resistor from pin 2 to pin 3 (euro side) trying to fake out the bulb.

    Please let me know if you found anything


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