I did my Alternator belt yesterday because it snapped on Saturday night, i'm very sunburnt from doing it, blisters and everythign oops. I used this guide : Audi B6 S4 DIY: Serpentine Belt / Service Position / Snub Mount and the job went smoothly. Whilst I had the bumper off I noticed a little compartment in it with a plug form the loom going to it but nothing there. I'm just curious what it is for ? Thanks.