I've had this car for about a month or so, a 2004 A6 2.7 automatic. About a week into ownership I noticed the brake lights would be on when I returned after parking. I read up and according to popular belief it wasa faultybrake sensor. I would usually be able to get the lights off by playing with the brake pedal. One night when this didn't work, I went into the fuses and removed to one for the brake lights(was that a stupid thing to do?). I put the fuse back in, there was a tiny spark and the problem hasn't been back at all, so Ihaven't yet replaced the brake sensor. Now at exactly, not almost or around, at exactly 125K, when I applied the brake I heard an internal click (sounded like a sensor engaging) and the 2 warning indicators lit up and now light up everytime the brake is first applied after a start. Is this just a coincidence orby a cruel design?

 

The only problem your having is a brake light swtich. The switch is a common problem on B6 and on A4's and all A6 models up to 2005. The common problems with the switch is:
Brake lamps staying on, no brake lamp illumination, abs activating under slight pedal effort, and even transmission limp mode.
Its the switch directly above the brake pedal, remove the trim under the steering wheel and you can see it.
Its VERY easy to break the switch when installing them so be carefull. When installing the switch don't touch the brake pedal and push and twist the switch into place until it locks. Verify correct operation of the brake light switch. If the brake lights are illuminated after the install without pushing the pedal take the switch out and pull the anchor on the switch fully out and try again.

 

Thanks 79. Installed it and all is well for now. Wasn't too difficult.