Mercedes-Benz 350SDL Back Up Light Bulb Size

The Mercedes-Benz 350SDL back up light requires a bulb with the unique P21W size. Data for the specific bulb requirements covers the range from 1990 to 1991.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1990-1991	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The P21W is the specified back up light bulb for the Mercedes-Benz 350SDL across the 1990-1991 model years.
The P21W follows the ECE (Economic Commission for Europe) standard, a regulatory framework adopted across Europe and numerous other markets worldwide.
This bulb operates on a 12-volt electrical system and draws 21 watts, which is typical for single-filament signalling applications.
The P21W uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin offset, distinguishing it from dual-contact bayonet variants.
Because the BA15s base is a single-contact design, it is not interchangeable with BA15d bulbs, which carry two contact pins and serve different circuit configurations.
The single-filament construction of the P21W means it serves one dedicated function, in this case the reverse light circuit, rather than combining multiple lighting roles within one bulb.