My 2000 A6 has the fog lights set up so they can only come on with the low beams per USDOT regs. Well, in Europe, they can come on with only the parking lights, which is nice in thick fog to reduce back glare(Irionically, many domestic vehicles come setup so the fogs can come on with only the parking lights.). This how-to is a variation on a tech article availible on www.AudiWorld.com I decided to do it a little differently than the author of the article, but credit him for coming up with the basic concept.
The major difference in the way I decided to do this mod is instead of using fuse taps, I created a different source for the feed side of the fog light fuse (36).
I wanted the fogs to only be able to come on with the parking lights (which is actually set by the switch mechanically.. You can't pull it to fogs in the off position) so I used the parking light feed. Since this is a low current curcut, not up to the task of powering the fogs, I used it as a trigger for a relay.