The Mercedes-Benz 450SEL uses a P21/5W bulb size for front turn signals and a P21W bulb size for rear turn signals. 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 450SEL 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 used in Europe and worldwide markets.
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 do not require a secondary function.
The BAY15d base of the P21/5W and the BA15s base of the P21W are not interchangeable. The BAY15d base has offset pins to ensure correct orientation of the dual filaments, while the BA15s base has symmetrical pins for a single-filament configuration.
The front turn signal position on the Mercedes-Benz 450SEL calls for the P21/5W across all model years from 1973-1980, indicating a consistent dual-filament requirement for that position throughout the vehicle's production run.
The rear turn signal position uses the P21W across all model years from 1973-1980, reflecting a consistent single-filament specification for that position.
Substituting a P21W in place of a P21/5W in the front turn signal position would result in the loss of the secondary 5W filament function, as the P21W carries only one filament.
Both the P21/5W and P21W operate on a 12V electrical system, which is consistent with the standard automotive voltage used in the 450SEL.