The Porsche 928 brake light utilizes P21W and P21/4W bulb sizes for illumination across various production versions. Available data covers the specific time range from 1978 through 1995.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Porsche 928 brake light circuit relies on two ECE-standard bulb types across its production run: the single-filament P21W and the dual-filament P21/4W.
The P21W is a single-filament bulb rated at 12V and 21W, mounted on a BA15s bayonet base. It is the predominant brake bulb type across the Porsche 928 lineup, appearing in the standard brake position from 1978-1990 and again in 1994-1995, as well as in the center high mount stop light from 1981-1994.
The P21/4W carries a dual-filament design rated at 12V with outputs of 21W and 4W, and it uses a BAZ15d bayonet base. The BAZ15d base is offset, meaning the two pins sit at different heights to prevent incorrect installation.
The P21W and P21/4W use different bayonet bases, BA15s and BAZ15d respectively, making them physically non-interchangeable despite their similar appearance and shared 21W output on the primary filament.
The Porsche 928 standard brake position specifies the P21/4W for the 1991 and 1993 model years, while surrounding years in that period use the P21W, indicating a fitment distinction that requires attention when sourcing a replacement for those specific years.
The center high mount stop light position on the Porsche 928 uses the P21W exclusively across all listed model years from 1981-1994, with no variation in bulb type for that position.
Both the P21W and P21/4W conform to ECE regulations, a framework recognized across Europe and numerous other markets worldwide, reflecting the international standards applied to the 928's lighting components.