The Audi V8 Quattro brake light utilizes a P21/5W bulb size for the specific lighting component located at the rear of the vehicle. Data for the bulb size covers the range from 1990 to 1994.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi V8 Quattro uses the P21/5W bulb for its brake lights across the full 1990-1994 production run.
The P21/5W is an ECE-standard dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The dual-filament design of the P21/5W allows a single bulb to serve two lighting functions, with the lower-wattage filament typically handling tail light duty and the higher-wattage filament handling the brake signal.
The BAY15d base features offset pins, which physically prevents incorrect single-filament bulbs from being seated in the socket, making filament-position orientation a critical fitment factor.
The center high mount stop light on the Audi V8 Quattro uses the 12961 bulb across the full 1990-1994 model range.
The 12961 is a Philips part number designating a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W.
The T10 wedge base is a single-filament design, which is consistent with the center high mount stop light function of operating at a fixed intensity rather than dual-level output.
The P21/5W and the 12961 use entirely different base types, a bayonet fitting versus a wedge fitting, making the two bulbs non-interchangeable with each other.