For kipilidisHi see the attached photo it shows the Connecter from the VW Quadlock to the block connecter which fits in the head unit.
It has 3 free wires.(you can only make out one in this pic)
a) The blue one is a 12v supply for arial adapters and arial line amplifiers only
b) the pinkish one you can just see on the attached picture is for a dimming circuit (see mrx's post on this)
c) a brownish one is for the rear view camera (and we are not clear on its operational function yet)
So the Blue free wire is the acc connector and it gives out +12v when the unit is on
For the full pin out functions see the post on p51
I don't know if yours is different, but mine has:
a) A Blue wire (p-cont) that supplys 12V whenever the headunit is on. Traditionally this is used for supplying power to an electric aerial or the turn on signal for an external power amplifier (sub woofer amp) etc. Only the turn on signal, not the main source of power - it wouldn't be able to supply enough current for that. There is no reason you couldn't use it to power you aerial amplifier as the current drawn by that would be small.
b) A Pink (illum) wire. Should have no/a very small voltage on it. If you connect it to ground the button lighting will turn off, if you connect it to 12V the buttons will illuminate at maximum brightness. If you connect it to anything between 0 & 12V the brightness will vary accordingly.
c) A Red (ACC) wire. I have not measured this one as I had no need for it, but traditionally this would have no/a small voltage on it. In most cars, where you have an Off, Accessory, On & Start position on your ignition key you would connect this to a source of 12V that is only present when the key is in the accessory position. Then the radio comes on whenever the key is turned to the accessory position and beyond. (ie. it is the turn on signal for the headunit). In the golf there is no accessory position, and the information is obtained from the canbus anyway, so it's a mystery to me why they've brought it out.
d) In my wiring loom, the brown wire was already connected to earth. (A bit naughty). You are supposed to connect this to the handbrake, so that you can only watch DVD's while the handbrake is engaged (ie. can't watch movies while you're supposed to be driving). This wire has nothing to do with the rear view camera. The sensing of reverse for the camera is done through the canbus. The unit automatically switches to the camera when reverse gear is engaged, but only if you actually have a camera connected to the camera video input.