The Audi 90 front side marker uses a P21/5W bulb with designation 12821, while the rear side marker requires a 12961 bulb size. The replacement chart covers vehicle production spanning 1988 to 1995 with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi 90 front side marker position uses two distinct bulb types across its model years: the P21/5W for 1993-1995 and the 12821 for 1988-1991.
The P21/5W is a dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. It follows ECE standards used in European and worldwide automotive applications.
The BAY15d base features offset pins, which physically prevents the bulb from being seated incorrectly, ensuring the two filaments are connected to the correct circuits.
The 12821 is a Philips-numbered miniature wedge bulb of the T10 form factor, rated at 12V and 5W, with a W2.1x9.5d wedge base. It is a single-filament bulb.
Because the P21/5W uses a BAY15d bayonet base and the 12821 uses a W2.1x9.5d wedge base, the two front side marker bulb types are not interchangeable with each other.
The rear side marker position on the Audi 90 uses the 12961 across all listed model years from 1988-1995, making it the only bulb type specified for that position.
The 12961 shares the same T10 form factor, W2.1x9.5d wedge base, 12V rating, and 5W output as the 12821, both being Philips part numbers for miniature wedge bulbs.
Although the 12821 and 12961 share the same base type and electrical ratings, they are listed under separate Philips part numbers, and substitution between them is not indicated by the specifications.