The Audi Coupe brake light requires a P21W bulb size for proper illumination and safety during vehicle operation. Data for the specified lighting component covers the range from 1981 to 1987.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi Coupe uses the P21W bulb for its brake lights across the 1981-1987 model years.
The P21W is an ECE-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, a single-contact base type commonly used in signalling applications.
The BA15s designation indicates a single-contact bayonet cap with a 15mm base width, which is distinct from the dual-contact BA15d variant and the two are not interchangeable.
The center high mount stop light on the Audi Coupe uses the 12961 bulb for the 1985-1987 model years.
The 12961 is a Philips part number referencing a miniature wedge-type bulb in the T10 form factor, rated at 12V and 5W, with a W2.1x9.5d wedge base.
The W2.1x9.5d base is a wedge-style fitting held in place by spring tension rather than a locking mechanism, making it physically incompatible with bayonet or screw-base sockets.
The P21W and the 12961 serve different functions and operate at different wattages, 21W and 5W respectively, and are not interchangeable with one another.
The two bulb types also use entirely different base designs, the BA15s bayonet and the W2.1x9.5d wedge, which prevents cross-fitting between the brake light and center high mount stop light sockets.