The Mercedes-Benz S320 brake light uses P21/5W and P21/4W bulb sizes according to the provided technical data for the specific lighting components. The information covers a production range from 1994 through 1999 for the specified vehicle and lighting system.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz S320 uses two distinct bulb types across its brake light positions: P21/5W and P21/4W for the standard brake lights, and H21W for the center high mount stop light.
The P21/5W is a dual-filament ECE-standard bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The P21/4W shares the same ECE dual-filament design as the P21/5W but carries a lower-rated secondary filament at 4W and uses a BAZ15d bayonet base rather than a BAY15d.
The BAY15d and BAZ15d bases are physically distinct, as the offset pins on each base are positioned differently to prevent incorrect bulb installation. The P21/5W and P21/4W are therefore not interchangeable despite their similar appearance and wattage ratings.
The Mercedes-Benz S320 brake lights for model years 1995-1999 require the P21/5W bulb, while the 1994 model year requires the P21/4W.
The H21W is a single-filament ECE-standard bulb rated at 12V and 21W, fitted with a BAY9s base, and is used exclusively in the center high mount stop light position.
The BAY9s base of the H21W is a smaller bayonet fitting that is incompatible with the BAY15d and BAZ15d bases used in the standard brake light positions.
The center high mount stop light on the S320 uses the H21W bulb across model years 1996-1999.
All three bulb types in these specifications conform to ECE regulations, indicating they are designed for use in European and worldwide markets rather than SAE-standard North American applications.