The Mercedes-Benz 450SL 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 vehicle production spanning 1973 to 1980.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz 450SL uses two distinct bulb types across its turn signal positions: the P21/5W for the front and the P21W for the rear, both conforming to ECE standards recognized in Europe and worldwide.
The P21/5W is a dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. The dual-filament design allows a single bulb to serve two lighting functions simultaneously.
The P21W is a single-filament bulb rated at 12V and 21W, mounted on a BA15s bayonet base. Its single-filament construction is suited to dedicated turn signal applications that require no secondary function.
The BAY15d base of the P21/5W and the BA15s base of the P21W are not interchangeable. The BAY15d features offset pins to ensure correct dual-filament orientation, while the BA15s uses a single-contact, symmetrical pin arrangement.
The front turn signal position on the 450SL requires the P21/5W across the full 1973-1980 model range.
The rear turn signal position on the 450SL requires the P21W across the full 1973-1980 model range.
Because the P21W and P21/5W share the same 21W primary wattage, they may appear physically similar, but their base types differ and substitution between the two positions is not supported by these specifications.