Okay, I could not find anything in the manual on this, so I thought I would put it out there for the group:

I have found (during that last look into the garage before bedtime) a tiny push-button switch on my 2002 Carrera 4 cabrio, located on the mount to the rear-view mirror, very near to its attachment point to the windshield. It is tiny, and is on the driver's side of the mount. I noticed a faint light coming from under the mirror when I looked into the dark garage last night, and thought I had inadvertently left one of the map lights on, but is it very faint, almost amber. It appeared to be 'on'. When I depressed the tiny button, it got BRIGHTER, then more faint when I pushed it again. There is nothing in the manual. Anybody have any clues??

 

The button changes the brightness of the LED cabin ambient lights, designed to put a subtle amber light on the center console near the gearshift at night.