Mercedes-Benz 380SL Back Up Light Bulb Size

The Mercedes-Benz 380SL back up light requires a P21W bulb size for proper installation and function. Data for the specific component covers the range from 1981 to 1985.

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
1981-1985	P21W

Bulb Specifications

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

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Additional Notes

The Mercedes-Benz 380SL uses the P21W bulb for the back up light position across all listed model years, 1981-1985.
The P21W is an ECE-standard bulb, meaning it conforms to the European and international regulatory framework for automotive lighting rather than the SAE standards common in North American vehicles.
P21W operates at 12 volts with a 21-watt output, which is a typical rating for single-filament signalling applications such as reverse lights.
The single-filament design of the P21W means it serves one lighting function only, distinguishing it from dual-filament bulbs that handle two functions, such as combined stop and tail duties.
The P21W uses a BA15s bayonet base, where "BA15" refers to the 15mm pin spacing of the bayonet cap and "s" denotes a single contact at the base, consistent with its single-filament construction.
The BA15s bayonet mount is not interchangeable with the BA15d base, which carries two contacts for dual-filament bulbs. Substituting a BA15d bulb in a BA15s socket is not a compatible fitment for the 380SL.
The P21W designation follows the ECE naming convention, where "P" indicates a single-filament bulb, "21" refers to the wattage, and "W" denotes a clear or white glass envelope.