Mercedes-Benz 450SE front turn signal bulbs use P21/5W size while rear turn signal bulbs use P21W size. The replacement chart covers 1973 through 1976 model years 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 Mercedes-Benz 450SE uses two distinct bulb types across its turn signal system for the 1973-1976 model years: the P21/5W at the front and the P21W at the rear.
The P21/5W is a dual-filament bulb rated at 12V with a 21W primary filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The BAY15d base features offset pins, a design that prevents incorrect insertion by ensuring the bulb can only be seated in one orientation.
The P21W is a single-filament bulb rated at 12V and 21W, mounted on a BA15s bayonet base, which uses a single contact pin in a symmetrical arrangement.
Both bulb types conform to ECE standards, a regulatory framework recognized across Europe and numerous other markets worldwide.
The front turn signal position on the 450SE calls for the P21/5W across all four model years, while the rear turn signal position calls for the P21W across the same span.
The P21/5W and P21W are not interchangeable despite sharing the same 21W primary wattage rating, as they differ in base type, pin configuration, and filament count.
Substituting a P21W into a front turn signal socket designed for a P21/5W BAY15d base would be physically incompatible due to the differing bayonet pin arrangements.