Mercedes-Benz 250SL front and rear turn signal bulbs utilize a P21W size across both positions. The replacement chart covers vehicle production spanning 1966 to 1968.
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 250SL across all listed turn signal positions and model years, covering both front and rear applications from 1966-1968.
The P21W is a single-filament bulb, meaning it serves one lighting function only. This distinguishes it from dual-filament types such as the P21/5W, which handle two functions, such as combined stop and tail duties, through a second filament.
The P21W operates on a 12-volt electrical system and draws 21 watts, which is the standard wattage for dedicated turn signal and brake light applications under ECE regulations.
The BA15s designation refers to a single-contact bayonet base with a 15mm collar. The single-contact design is a direct consequence of the single-filament construction, as only one electrical contact is required.
The P21W conforms to ECE (Economic Commission for Europe) standards, a regulatory framework adopted across Europe and numerous other markets worldwide. This origin reflects the 250SL's primary market positioning.
Because the front and rear turn signal positions on the 250SL share the same P21W specification for all listed years, the bulb is interchangeable between those positions without modification.
The BA15s bayonet base is not interchangeable with the BA15d base, which is a dual-contact variant of the same 15mm bayonet fitting. Substituting a BA15d bulb in a BA15s socket is not mechanically compatible without adapter hardware.