thebishop

Having read numerous posts, and needing a trailer brake controller, I bought a Tekonsha P3. Pulled the kick panel off (after reading another post about the hidden screw above the steering column), and found the 4-pin connector that I'm sure I should be wiring the P3 into.

However, when I tested it, I found this:
Pin 1: +12v
Pin 2: Ground
Pin 3: Connection to pin 2 ("blue") on trailer connector (good so far)
Pin 4: er, Nothing? I expected this to be +12V when pressing on the brake pedal. Am I missing something?

Jusforfun

pretty sure it just uses three of the pins. + and - to feed power to unit and blue is varying voltage going from car to trailer and tekonsha unit.
Not totally sure but I think you vary trailer brake by changing resistance on blue at unit.
Did you check blue for varying voltage as you press brake pedal?

I suspect electric brakes would work without the unit but you couldnt adjust or see what going on.

thebishop

I'm pretty sure the P3 needs the brake signal to determine whether your foot is on the brake, and an internal accelerometer (hence the need to install the unit in the right orientation) to determine how much braking to apply. But that should mean that one of the pins senses the brake signal. Maybe the Q5 doesn't put voltage on that pin unless a trailer is plugged into the connector?

Here's etrailer's diagram showing the red wire connected to the brake switch:
http://www.etrailer.com/Merchant2/gr...qu6890_800.jpg

thebishop

In case anyone cares, the part numbers are as follows:
1J0 972 772 (plug in the car already)
1J0 972 782 (it's mate) (buy one)
000 979 228 (contacts w/ wires for the plug) (buy two)

There's also a tech article from Tekonsha here; very close to the Q5 install:
http://tm-techmark.com/touareg/PDFfiles/Tip 2 Volkswagen Touareg Porsche Cayenne.pdf