Mercedes-Benz S550 Back Up Light Bulb Size

The Mercedes-Benz S550 back up light utilizes 921 and 12184 bulb sizes for the rear illumination system. Data for the specific components covers the period from 2007 through 2013.

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
2009-2013	921
2007-2008	12184

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
Philips part number. Halogen bulb, specialty application. 12V.	12184

Other Locations

Additional Notes

The Mercedes-Benz S550 back up light specifications cover model years 2007-2013, spanning two distinct bulb types across that range.
The 921 is an ANSI-standardized bulb used in the United States and Canada, classified as a T15 wedge type operating at 12 volts and 16 watts.
The T15 designation refers to the bulb's tubular shape, with the numeric portion indicating its width in eighths of an inch, and the wedge base design allows direct insertion into a socket without a separate metal base or pins.
The 12184 is a Philips part number rather than an industry-wide standard designation, identifying it as a halogen bulb rated for specialty applications at 12 volts.
The Mercedes-Benz S550 used the 12184 bulb for model years 2007-2008, after which the specification shifted to the 921 for model years 2009-2013.
Because the 12184 is a specialty halogen type and the 921 is a standard wedge bulb, the two are not interchangeable despite sharing a 12-volt operating voltage.
The 921 bulb's ANSI standardization means it is produced by multiple manufacturers under the same designation, whereas the 12184 is tied to Philips' own product numbering system.