Audi 100 front turn signal bulbs use P21/5W size while rear turn signal bulbs use P21W size. The replacement chart covers 1989 to 1994 model years 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 100 uses two distinct bulb types across its front and rear turn signal positions, with the P21/5W assigned to the front and the P21W assigned to the rear for the 1989-1994 model years.
The P21/5W is a dual-filament bulb, meaning it carries two separate filaments within a single envelope, rated at 21W and 5W respectively on a 12V circuit.
The P21W is a single-filament bulb rated at 21W on a 12V circuit, serving a dedicated signalling function without a secondary filament.
Both bulb types conform to ECE standards, which are recognized across Europe and internationally, and both operate on a 12V electrical system.
The P21/5W uses a BAY15d bayonet base, which is an offset twin-pin fitting. The offset pin arrangement prevents the bulb from being seated in the wrong rotational position.
The P21W uses a BA15s bayonet base, which is a single-pin fitting. This base is not interchangeable with the BAY15d used by the P21W, as the pin configurations differ.
Because the front turn signal on the Audi 100 (1989-1994) uses a dual-filament P21/5W, the housing is designed to utilize both filaments, and substituting a single-filament bulb such as the P21W would be incompatible regardless of any physical fitting similarity.
The consistent bulb specifications across all six model years indicate that no housing or electrical changes affected bulb fitment within the 1989-1994 production span of the Audi 100.