Mercedes-Benz R350 Back Up Light Bulb Size

The Mercedes-Benz R350 back up light uses 921 and P21W bulb sizes according to the provided data. Information for the specified components covers the range from 2006 to 2012.

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
2011-2012	921
2006-2010	P21W

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The Mercedes-Benz R350 backup light specifications reference two distinct bulb standards across its model years: the 921, which follows the ANSI standard used in the United States and Canada, and the P21W, which follows the ECE standard used in Europe and worldwide markets.
The P21W is the more frequently specified bulb across the R350 lineup, covering the 2006-2010 model years for the backup light position.
The 921 bulb is specified for the 2011-2012 R350 model years, representing a shift from the ECE-standard P21W used in earlier years.
The 921 is a T15 wedge-base bulb, meaning it is held in its socket by friction rather than by a locking mechanism, and operates at 12 volts with a 16-watt output.
The P21W uses a BA15s bayonet base, a single-contact fitting that locks into its socket with a quarter-turn motion, and operates at 12 volts with a 21-watt output.
The P21W carries a higher wattage rating of 21 watts compared to the 921 at 16 watts, and the two bulbs use physically incompatible base types, making them non-interchangeable despite sharing the same 12-volt operating voltage.
The P21W is a single-filament bulb, a construction type associated with dedicated signalling functions such as backup lighting, where only one brightness level is required.