Audi 100 front and rear side marker bulbs utilize a 12821 bulb size for this model. The replacement chart covers vehicle production spanning 1989 to 1994.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi 100 uses the 12821 bulb across both its front and rear side marker positions for the 1989-1994 model years.
The 12821 is a Philips part number designating a miniature wedge bulb in the T10 form factor, rated at 12 volts and 5 watts.
The T10 designation refers to a tubular bulb with a width of approximately 10 millimeters, commonly found in low-intensity automotive lighting applications such as side markers and parking lights.
The W2.1x9.5d base type on the 12821 is a wedge-style connector, meaning the bulb is held in place by tension from the socket rather than by a bayonet or screw mechanism.
Because the Audi 100 uses the same 12821 bulb for both the front and rear side marker positions, a single bulb type services all four side marker sockets on the vehicle.
The 5-watt power rating of the 12821 places it in the low-wattage category typical of marker and courtesy lighting, as opposed to higher-wattage bulbs used in headlamps or brake lights.
The W2.1x9.5d base specification is a standardized IEC designation, where 2.1 refers to the wire contact width in millimeters and 9.5 refers to the wedge length in millimeters, making cross-referencing with non-Philips equivalents possible using these values.