[Brandish]

It's doubtful there's anything useful in that cable outside of VW factory equipment... It's not simply an "aux in" for the factory HU, there's probably data lines that the deck uses to communicate with the changer, so there's probably no way to get the factory HU to recognize that there's even anything connected to the changer input. You're better off going with an FM mod, or replacing the factory HU with a deck that has aux in.