Mercedes-Benz 450SLC Back Up Light Bulb Size

The Mercedes-Benz 450SLC back up light requires a P21W bulb size for proper illumination. Data for the specified component covers the period from 1973 through 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 450SLC 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 regulatory framework, which governs automotive lighting across European and many worldwide markets.
The P21W operates at 12 volts and 21 watts, placing it in the range typical for single-filament signalling applications such as reverse and turn signal functions.
A single filament design means the P21W serves one lighting function only, as opposed to dual-filament bulbs that handle two functions, such as combined stop and tail duties, within a single unit.
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 base type 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.