Mercedes-Benz 300SEL Back Up Light Bulb Size

The Mercedes-Benz 300SEL back up light utilizes a P21W bulb size for illumination. Data for the specific component covers the range from 1969 through 1991.

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
1988-1991	P21W
1969-1973	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 300SEL uses the P21W bulb size across all listed model years for the back up light position.
The P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe regulatory framework used in European and worldwide automotive lighting applications.
P21W bulbs operate on a 12-volt electrical system and draw 21 watts, which is typical for single-filament signalling applications such as reverse lights.
The P21W uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin offset, distinguishing it from dual-contact bayonet variants that are not interchangeable with it.
Because the BA15s base is a single-contact design, substituting a dual-contact bayonet bulb such as the BA15d would result in an incompatible fitment.
The P21W designation covers model years 1969-1973 and 1988-1991 on the 300SEL, representing two distinct production periods separated by a gap in the listed data.
The single-filament construction of the P21W means it serves one lighting function only, which is consistent with its use in a dedicated back up light circuit rather than a combined stop and tail application.