The Porsche 944 brake light requires a P21W bulb size for proper installation and function within the rear lighting assembly. Available data covers the production span from 1983 through 1991.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Porsche 944 uses the P21W bulb for brake lighting across all model years covered in the specifications, spanning 1983-1991.
The P21W is an ECE-standard single-filament bulb rated at 12 volts and 21 watts, designed primarily for signalling applications such as brake and stop lights.
P21W bulbs use a BA15s bayonet base, which is a single-contact bayonet fitting. The "s" in BA15s denotes a single offset pin, distinguishing it from the dual-contact BA15d variant.
The BA15s base type is not interchangeable with BA15d bases. Substituting one for the other is not possible without a socket adapter, as the pin configurations differ.
Both the standard brake light position and the Center High Mount Stop Light on the Porsche 944 share the same P21W specification across 1983-1991, meaning both positions draw from the same bulb type.
The P21W designation follows ECE (Economic Commission for Europe) naming conventions, indicating the bulb meets internationally recognized standards for automotive signalling use rather than SAE standards common in North American markets.
At 21 watts, the P21W produces a relatively high output for a single-filament signal bulb, which is a characteristic intentional to the stop light function where high visibility is a priority.
Because the P21W is a single-filament bulb, it serves only one function per socket. Positions requiring combined tail and brake functions use separate dual-filament bulbs in other applications, though the 944 specifications here reference only the single-filament type.