I believe there is a separate wiring assemble with a control module to facilitate trailer power.
Here in the UK I have fitted the 13 pin power connector rather than the basic 7 pin and I guess that provide for additional auxiliary power but I don't use it for anything other than a small trailer for bikes etc...
Q7 4.2Tdi S-Line 2008 - another V8 diesel!
A8 4.2Tdi, 06, Grey/Grey - my new toy - how can a diesel be this fast? SOLD 21/06/2013
2010 A4 2.0tdi 6 spd SE Executive avant - dark blue & Vanilla - Wife's new one.
VW Touareg 06 30k 6spd 2.5Tdi - Wifey's new one, A4 was not big enough!
A6 2.7t 01my 6spd Avant 51k miles - Sold Dec 2011 - Gone to Banbury
A4 2.0FSi SE 03.8 22k miles - Wifey's new one - the golf was not luxurious enough. Sold 30/08/08 - gone to Heathrow.
Golf Tdi 03.08 130pd, 6spd, 19k miles - Sold 8th November 2006 - gone to Coventry!
A6 2.8q 98.11 115K miles - sold 20th Feb 2006 - gone to Kidderminster.
100 2.8q 92.1 147k miles - Sold 6th July 2004 - its new home is Edinburgh
A4 1.6 97.8 99k miles - Sold 12th Feb 03
VW Golf Gti 86 22k miles 2.0 Oettinger 190bhp, lowered, lightened and quick and sold 23/03/08. Gone to Coventry.