Mercedes-Benz 280S front turn signal bulbs use P21/5W size while rear turn signal bulbs use P21W size. The replacement chart covers vehicle production spanning 1968 to 1976.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz 280S uses two distinct bulb types across its front and rear turn signal positions: the P21/5W for the front and the P21W for the rear, across model years 1968-1971 and 1975-1976.
Both the P21/5W and P21W are ECE-standard bulbs, meaning they conform to the Economic Commission for Europe regulatory framework used in European and worldwide automotive lighting applications.
The P21/5W is a dual-filament bulb, operating at 12 volts with two wattage ratings: 21W for the primary filament and 5W for the secondary filament. This dual-filament design allows a single bulb to serve more than one lighting function simultaneously.
The P21/5W uses a BAY15d bayonet base. The BAY15d designation indicates an offset dual-contact base, where the two pins are positioned at different heights to prevent incorrect installation.
The P21W is a single-filament bulb rated at 12 volts and 21 watts, dedicated solely to the turn signal function at the rear of the vehicle.
The P21W uses a BA15s bayonet base, which is a single-contact base with symmetrically placed pins. This base type is not interchangeable with the BAY15d base found on the P21/5W, as the pin configurations differ.
Because the front position requires a P21/5W and the rear requires a P21W, the two bulb types serve different roles and cannot be substituted for one another despite sharing the same 21W primary output rating.