Mercedes-Benz GL550 Back Up Light Bulb Size

The Mercedes-Benz GL550 back up light uses 921 and P21W bulb sizes for the rear illumination components. Data for the specific lighting requirements covers the period from 2008 through 2016.

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
2013-2016	921
2008-2012	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 GL550 backup light bulb specifications cover model years 2008-2016, split across two distinct bulb types depending on the year.
The 921 bulb follows the ANSI standard, which is the governing specification used in the United States and Canada. It is a T15 wedge-base bulb rated at 12 volts and 16 watts.
The P21W bulb follows the ECE standard, the regulatory framework used in Europe and most of the world. It is a single-filament signalling bulb with a BA15s bayonet base, rated at 12 volts and 21 watts.
The GL550 uses the 921 bulb for model years 2013-2016.
Model years 2008-2012 of the GL550 use the P21W bulb.
The two bulb types are not interchangeable. The 921 uses a wedge base while the P21W uses a BA15s bayonet base, meaning the physical mounting mechanisms are fundamentally different.
There is also a wattage difference between the two types. The P21W draws 21 watts versus the 921 at 16 watts, reflecting a difference in power consumption that may be relevant to socket and circuit compatibility.
The base type change between the P21W and the 921 corresponds to a shift from ECE-standard to ANSI-standard components, which aligns with a broader industry practice of regionalizing bulb specifications by market.