Well I found a thread over on vwvortex with the mk6 steering wheel pinout and it's kind of making a little bit of sense now.
http://www.vwwatercooled.com.au/foru...c85d9png-1.jpg
So for the yellow connector (F350), pinout as follows:
Pin 3: Airbag
Pin 4: Airbag
Pin 7: Ground
Pin 8: Horn
Pin 9: Lin bus
Pin 10: 12V
For the black connector (J453):
Pin1: GND
Pin2: 12V
Pin3: Lin
Pin4: Horn (in)
Pin5: Horn (out)
The horn signal looks like it may go via Lin as well as its own signal.
Now all I need is the pinout for the Mk7 Steering wheel control unit (black connector) and I should be able to get this sorted....