I read somewhere that there are issues with just tapping into the stock wiring. SVXdc sells the harness with the extra wires for 13 bucks and he is pretty fast. I ordered mine last night around 7pm and within a few hours i had an email with the ordering information.
He will also sell you the Axxess ASWC with updated firmware which a lot of places do not do. (his price is cheeper than sonicelectronix)
If you plan to use your stock AUX port in the center armrest console he sells a piece for that as well.