Mercedes-Benz S600 Back Up Light Bulb Size

The Mercedes-Benz S600 back up light utilizes bulb sizes 921, 12184, and P21W depending on the specific version of the vehicle. Available data for the lighting components covers a range from 1994 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
2001-2006	P21W
1994-1999	P21W

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
Philips part number. Halogen bulb, specialty application. 12V.	12184
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The Mercedes-Benz S600 back up light specifications reference three distinct bulb types across the 1994-2013 model years: the 921, the 12184, and the P21W.
The P21W is an ECE-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base. It is the bulb type specified for the S600 across the greatest number of model years, covering 1994-1999 and 2001-2006.
The 921 is an ANSI-standard wedge-type bulb in a T15 form factor, rated at 12V and 16W. It is specified for the S600 from 2009-2013.
The 12184 is a Philips part number designating a 12V halogen bulb for specialty applications. It is specified for the 2007-2008 S600.
The P21W and the 921 are not interchangeable. The P21W uses a BA15s bayonet base, while the 921 uses a wedge-type base, making the two physically incompatible without modification.
The 12184 and the 921 also differ in construction, as the 12184 is a halogen bulb while the 921 is a standard incandescent wedge type, and the two serve different socket configurations.
The wattage difference between the P21W at 21W and the 921 at 16W means the two bulbs draw different amounts of current, which is a relevant consideration for electrical compatibility in addition to the physical base difference.
The shift from the P21W to the 12184 between the 2006 and 2007 model years reflects a change in the bulb standard used, moving from an ECE-designated type to a manufacturer-specific Philips part number.
The subsequent shift from the 12184 to the 921 between the 2008 and 2009 model years represents a further change, this time to an ANSI-standard wedge bulb common in the North American market.