Mercedes-Benz 250 Back Up Light Bulb Size

The Mercedes-Benz 250 back up light requires a P21W bulb size for proper installation and function within the rear lighting assembly. Available data for the specified component covers the period from 1968 through 1973.

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
1968-1973	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 250 uses the P21W bulb as the specified back up light bulb size across all listed model years from 1968 to 1973.
The P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe's regulations, which govern lighting equipment used in European and worldwide automotive markets.
The P21W operates at 12 volts with a 21-watt output, classifying it as a standard-wattage single-filament bulb suited for signalling applications such as reverse lighting.
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 lighting, within a single unit.
The P21W uses a BA15s bayonet base, where "BA15" refers to a 15mm bayonet cap and the "s" denotes a single-contact configuration, distinguishing it from the dual-contact BA15d variant.
The BA15s single-contact base is a fitment-critical detail, as substituting a BA15d dual-contact bulb into a BA15s socket is not mechanically compatible without modification.