[Gabe1]

I have a 1997 Audi A6 Quattro . Just recently i had replaced a brake
light bulb. Last night the tail light didnt come on. The brake lights
on both sides work as with the backup and signal lights. I have check
the fuses and replaced the " Tail " relay . Still the tail lights
doesnt come on with the head lights. why??? can someone explain me?

 

[bronco23]

I hope this doesn't sound too stupid but......assuming you are in the UK (although tail light sounds American) the brake light bulb and tail light bulb are one and the same bulb. So the single bulb is twin element and has two small soldered oval shapes on the base. If so, your problem could be as simple as having fitted the new bulb the wrong way around and therefore no contact is being made with the tail light feed.
Often you cn conncet them and the brake light activates with the tail light.
Sorry if this doesn't apply to your bulbs