Mercedes-Benz 420SEL Back Up Light Bulb Size

The Mercedes-Benz 420SEL back up light requires a P21W bulb size for proper installation and function. Data for the specified component covers the period from 1986 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
1986-1991	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 420SEL uses the P21W bulb for its back up light across all listed model years, spanning 1986-1991.
The P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe's lighting regulations, which are widely adopted across European and international vehicle markets.
This bulb operates on a 12-volt electrical system and draws 21 watts, which is typical for single-filament incandescent signalling applications.
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.
Because the BA15s base is a single-contact design, it is not interchangeable with the BA15d base, which carries two contacts for dual-filament bulbs.
The single-filament construction of the P21W means it serves one lighting function only, which is consistent with its role as a dedicated back up light bulb rather than a combined stop and tail unit.