Mercedes-Benz R500 Back Up Light Bulb Size

The Mercedes-Benz R500 back up light requires a bulb size of P21W for the rear illumination system. Data for the specified lighting component covers the range from 2006 to 2007.

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
2006-2007	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 R500 across the 2006-2007 model years.
The P21W is an ECE-standard single-filament bulb rated at 12 volts and 21 watts, designed primarily for signalling applications such as reverse lights.
The P21W uses a BA15s bayonet base, which is a single-contact bayonet mount with a 15mm collar. The "s" designation indicates a single contact point at the base, distinguishing it from dual-contact variants.
Because the BA15s base is a single-contact fitting, substituting a dual-contact bayonet bulb such as the BA15d would result in an incompatible fitment for the R500 back up light socket.
The P21W designation follows ECE (Economic Commission for Europe) naming conventions, reflecting its origin as a globally recognized standard rather than a manufacturer-specific part number.