Below is a list of light bulb types used in 2004-2008 AUDI A4 lighting system, covering estate and saloon 4-door vehicles.
Headlight bulb: low beam - H7 or D1S / high beam - H7 or D1S
Parking light bulb: W5W
Fog light bulb: H11
Front indicator/turn signal bulb: P21W or PY21W
Side direction indicator bulb: WY5W
Daytime running light bulb: P21W
Rear indicator/turn signal bulb: P21W
Tail light bulb: P21W
Brake light bulb: P21W
Back-up light bulb: P21W
Rear fog light bulb: P21W
License plate light bulb: C5W
Interior light bulb: C10W or C5W
Door safety light bulb: W5W
Boot light bulb: W5W
Entry light bulb: W5W
Footwell light bulb: W5W
Reading light bulb: T5W
Glove compartment light bulb: W5W or W3W
Light bulb sizes for other AUDI A4 generations: A4 (B5) / A4 (B6) / A4 (B8) / A4 (B9)