Below is a list of light bulb types used in 1997-2005 AUDI A6 lighting system, covering estate and saloon 4-door vehicles.
Headlight bulb: low beam - D2S, H1 or H7 / high beam - H7 or H9
Parking light bulb: W5W
Fog light bulb: H3 or H7
Front indicator/turn signal bulb: PY21W
Side direction indicator bulb: WY5W
Rear indicator/turn signal bulb: P21W
Tail light bulb: P21/5W
Brake light bulb: P21/5W
Back-up light bulb: P21W
Rear fog light bulb: P21W
License plate light bulb: C5W
Auxiliary stop light bulb: W2,3W
Door safety light bulb: W5W
Boot light bulb: C5W
Entry light bulb: W5W
Footwell light bulb: C5W
Glove compartment light bulb: C5W
Interior light bulb: C10W or C5W
Reading light bulb: T4W
Light bulb sizes for other AUDI A6 generations: A6 (C4) / A6 (C6) / A6 (C7)