The Mercedes-Benz 300SL uses a P21W bulb size for both front and rear turn signal applications. The replacement chart covers 1990 to 1993 model years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21W is the sole bulb type specified for the Mercedes-Benz 300SL across all listed turn signal positions and model years.
P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe regulatory framework used in European and worldwide automotive lighting applications.
The P21W operates at 12 volts and draws 21 watts, which is the standard wattage for single-filament automotive signalling applications.
The P21W uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin offset to one side, which prevents incorrect installation of polarity-sensitive bulbs.
As a single-filament bulb, the P21W is dedicated to one lighting function per unit, distinguishing it from dual-filament types such as the P21/5W, which serve two functions simultaneously.
The front and rear turn signals of the 300SL share the same P21W specification across the 1990-1993 model years, indicating a uniform bulb requirement for all four turn signal positions.
The BA15s bayonet base is not interchangeable with the BA15d base, which carries two offset pins. Substituting a BA15d bulb in a BA15s socket is not mechanically compatible.
The 21-watt rating of the P21W is a factor in turn signal flash rate, as the vehicle's flasher relay is typically calibrated to the expected load. Substituting a bulb of significantly different wattage may alter the flash frequency.