The Audi A8 brake light requires a P21/5W bulb size for proper installation and function. Data for the specific component covers the range from 1997 to 1999.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi A8 brake light position uses the P21/5W bulb across all listed model years from 1997-2003.
The P21/5W is an ECE-standard dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, making it suitable for combined stop and tail light functions within a single unit.
The P21/5W uses a BAY15d bayonet base, a two-pin offset base design that prevents incorrect installation by ensuring the bulb can only be seated in one orientation.
The Center High Mount Stop Light on the Audi A8 uses the 12961 bulb across all listed model years from 1997-2003.
The 12961 is a Philips part number designation for a T10 miniature wedge bulb rated at 12V and 5W, a significantly lower wattage than the P21/5W used in the main brake light position.
The T10 wedge bulb uses a W2.1x9.5d base, which is a pinless wedge-type connection held in place by contact tension rather than a locking mechanism.
The BAY15d base of the P21/5W and the W2.1x9.5d base of the 12961 are physically incompatible with each other, meaning the two bulb types are not interchangeable between positions.
The dual-filament construction of the P21/5W distinguishes it from the single-filament 12961, reflecting the different functional requirements of the main brake position versus the high mount stop light.