The Mercedes-Benz 300SEL front side marker uses a P21/5W bulb size, while the rear side marker requires a 3893 bulb size. The replacement chart covers vehicle production spanning 1969 to 1991 with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 3893 is the most frequently specified bulb across these side marker positions, appearing in both front and rear rear side marker roles across the 1969-1973 and 1988-1991 model years.
Both the P21/5W and the 3893 share a BAY15d bayonet base, which is a dual-contact offset-pin fitting designed to prevent incorrect installation by positioning the two pins at different heights on the base.
Both bulb types operate on a 12V electrical system and carry dual filaments, meaning each bulb serves two brightness levels within a single housing.
The P21/5W follows the ECE regulatory standard, which governs lighting equipment across European and various international markets, and is rated at 21W for its primary filament and 5W for its secondary filament.
The 3893 follows the ANSI standard used in the United States and Canada and is classified as a specialty application bulb within that system.
On the Mercedes-Benz 300SEL, the front side marker position for the 1988-1991 model years calls for the P21/5W, while the rear side marker position for those same years calls for the 3893, meaning the two positions are not interchangeable despite sharing a base type.
For the 1969-1973 model years, both the front and rear side marker positions use the 3893, making the bulb uniform across both positions for that generation.
Although the P21/5W and the 3893 share a BAY15d base, their differing wattage ratings and regulatory standards mean substituting one for the other carries compatibility risk, particularly in markets where ECE or ANSI compliance is required.