Mercedes-Benz R320 Back Up Light Bulb Size

The Mercedes-Benz R320 back up light requires a bulb with the specific P21W size for proper installation and function. Data for the bulb size covers the range from 2007 to 2009.

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
2007-2009	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 sole bulb type listed across all documented model years of the Mercedes-Benz R320, covering the 2007-2009 range for the back up light position.
The P21W follows the ECE (Economic Commission for Europe) standard, a regulatory framework adopted across Europe and numerous other markets worldwide.
As a single-filament bulb, the P21W is designed exclusively for on/off signalling functions, which aligns with the operational nature of a back up light.
The P21W operates at 12 volts and draws 21 watts, placing it in the standard incandescent range for automotive signalling applications.
The BA15s designation refers to a bayonet-style base with a 15mm collar and a single locating pin, which positions the filament at a fixed rotational angle within the housing.
The single-pin BA15s base is not interchangeable with the BA15d base, which carries two offset pins and is used on dual-filament bulbs. Substituting one for the other is not physically compatible.