Mercedes-Benz 560SEC front side marker bulbs use P21/5W size while rear side marker bulbs use 3893 size. The replacement chart covers 1986 through 1991 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz 560SEC uses two distinct bulb types across its front and rear side marker positions, with each position remaining consistent across the 1986-1991 model years.
The front side marker on the 560SEC calls for the P21/5W bulb, an ECE-standard type used across European and worldwide automotive markets.
P21/5W is a dual-filament bulb rated at 12V with separate 21W and 5W filaments, housed in a BAY15d bayonet base, which is an offset twin-contact fitting designed to prevent incorrect installation.
The dual-filament construction of the P21/5W allows it to serve two lighting functions within a single housing, with the higher-wattage filament typically handling the primary signal function and the lower-wattage filament handling a secondary or parking function.
The rear side marker on the 560SEC requires the 3893 bulb, an ANSI-standard type used in North American automotive applications.
The 3893 is also a dual-filament bulb operating at 12V and shares the BAY15d bayonet base with the P21/5W, though it is classified as a specialty application type under the ANSI standardization system.
Despite both the P21/5W and the 3893 sharing a BAY15d bayonet base, they are governed by different regional standards, ECE and ANSI respectively, and are specified for different positions on the vehicle.
The BAY15d base common to both bulb types features two pins at different heights on the base, a design that physically prevents the bulb from being seated in the wrong rotational orientation within the socket.