Have you had any other electrical problems? I think I remember reading you had a new TB fitted (my current problem) only say this because I've had the drivers switches and motor problems, had to swap them out... Does your alarm work? Had to swap that out too and the wiper motor, and the cruise control... Hmm.
There a big thread on Audizine that seems to suggest a lot of issues are caused by bad wiring/earthing or ECU.