Mercedes-Benz 450SL Back Up Light Bulb Size

The Mercedes-Benz 450SL back up light requires a P21W bulb size for proper illumination and function. Data for the specific component covers the range from 1973 to 1980.

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
1973-1980	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 450SL uses the P21W bulb across all listed model years, 1973-1980, for the back up light position.
The P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe's regulations, which govern lighting equipment used in Europe and numerous other markets worldwide.
P21W bulbs operate on a 12-volt electrical system and draw 21 watts, which is typical 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, corresponding to its single-filament construction.
The BA15s base is a keyed, single-contact fitting, which means it is not interchangeable with the BA15d base, a visually similar double-contact variant used on dual-filament bulbs.