This is the adapter you'll need... (or I have used in the 2008 JETTA)
C2R-VW <- All extra input you need: Illumination, VSS, and +12V Switched... You need this if you are not using SWI-PS
OR SWI-CAN <- Same thing as above, but need to use with SWI-PS below... Cheaper...
Choose ONE above...
AND SWI-PS <- Steering Wheel Buttons Control for Pioneer Headunit
The C2R-VW comes with VW harness adapter already... So the other thing you need is the Metra 40-EU55 antenna adapter...
enfigcarstereo.com have all the stuff you need to get the job done...
Pioneer does