Mercedes-Benz S320 Back Up Light Bulb Size

The Mercedes-Benz S320 back up light requires a P21W bulb size for proper installation and function. Available data for the specified component covers the period from 1994 through 1999.

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
1994-1999	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 Mercedes-Benz S320 uses the P21W bulb as the back up light bulb across all listed model years, spanning 1994-1999.
The P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe regulatory framework, which governs automotive lighting across European and many worldwide markets.
The P21W operates at 12 volts and 21 watts, which is a standard rating for single-filament signalling applications such as reverse lights.
The bulb uses a BA15s bayonet base, where "BA" denotes a bayonet cap fitting, "15" refers to the 15mm base width, and the lowercase "s" indicates a single contact at the base.
Because the P21W is a single-filament bulb, it serves one lighting function only, distinguishing it from dual-filament variants such as the P21/5W, which would not be a direct substitute.
The BA15s base type is not interchangeable with the BAY15d or BAZ15d bayonet bases, as those feature offset or dual contact pins designed for dual-filament bulbs.