The Mercedes-Benz 300SE brake light utilizes P21/4W and P21W bulb sizes for the rear lighting system. Data for the specific components covers the period from 1988 through 1993.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz 300SE uses two distinct bulb types across its brake light specifications: the P21W for model years 1988-1991 and the P21/4W for model years 1992-1993.
Both bulb types conform to ECE standards, which are regulatory specifications adopted across Europe and numerous other markets worldwide.
The P21W is a single-filament signalling bulb operating at 12 volts with a 21-watt output, mounted on a BA15s bayonet base.
The P21/4W is a dual-filament signalling bulb operating at 12 volts with filaments rated at 21 watts and 4 watts respectively, mounted on a BAZ15d bayonet base.
The BA15s and BAZ15d bayonet bases are not interchangeable. The BAZ15d base uses offset pins to prevent incorrect installation, while the BA15s base uses symmetrical pins.
Because the P21W and P21/4W use different base configurations, a P21/4W bulb cannot serve as a direct replacement for a P21W, and vice versa.
The transition from P21W to P21/4W in the brake light position between the 1991 and 1992 model years reflects a change in the socket and wiring configuration of the 300SE.
The Center High Mount Stop Light on the 300SE is specified for model years 1988-1991 only, using the P21W single-filament bulb throughout that range.