The Mercedes-Benz 420SEL brake light utilizes a P21W bulb size for the rear lighting system. Data for the specific 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.
The Mercedes-Benz 420SEL uses the P21W bulb across all brake light positions for the 1986-1991 model years.
The P21W is an ECE-standardized single-filament bulb rated at 12 volts and 21 watts, designed primarily for signalling applications such as brake and stop lights.
P21W bulbs use a BA15s bayonet base, which is a single-contact bayonet fitting with a 15mm collar.
The BA15s base designation indicates a single-contact configuration, distinguishing it from the dual-contact BA15d variant, which is not interchangeable with the 420SEL's brake light sockets.
The same P21W specification applies to both the standard brake lights and the Center High Mount Stop Light on the 420SEL across the full 1986-1991 production span.
The ECE designation on the P21W reflects compliance with United Nations Economic Commission for Europe regulations, a standard adopted across European and many international markets.
At 21 watts, the P21W produces a higher output than lower-wattage signal bulbs such as the P5W, which is a relevant distinction when sourcing replacements to maintain correct brake light intensity.