The Mercedes-Benz 300SDL uses a P21/5W bulb size for the front turn signal and a P21W bulb size for the rear turn signal. The replacement chart covers 1986 to 1987 model 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 300SDL uses two distinct ECE-standard bulb types across its front and rear turn signal positions for the 1986-1987 model years.
The front turn signal on the 300SDL takes a P21/5W bulb, which is a dual-filament type operating at 12V with a 21W primary filament and a 5W secondary filament.
The P21/5W uses a BAY15d bayonet base, a two-pin offset base design that prevents incorrect insertion by ensuring only one rotational orientation fits the socket.
The rear turn signal on the 300SDL takes a P21W bulb, which is a single-filament type rated at 12V and 21W.
The P21W uses a BA15s bayonet base, a single-pin design that differs physically from the BAY15d base found on the front turn signal bulb.
Because the P21/5W and P21W use different base types, the front and rear turn signal bulbs are not interchangeable with each other.
Both bulb types conform to ECE regulations, a lighting standard recognized across Europe and numerous other markets worldwide.
The shared 21W filament wattage between the P21W and the primary filament of the P21/5W produces equivalent light output for the active turn signal function at both the front and rear positions.