The Mercedes-Benz 450SLC 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 450SLC uses two distinct bulb types across its front and rear 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.
Both bulb types operate on a 12-volt electrical system, which was the standard automotive voltage for production vehicles of this era.
The P21/5W is a dual-filament bulb, meaning it serves two lighting functions within a single housing. It carries a 21-watt primary filament and a 5-watt secondary filament, making it suitable for combined signalling and position light duties.
The P21/5W uses a BAY15d bayonet base. The BAY15d designation indicates an offset dual-contact base, where the two pins are positioned at different heights to prevent incorrect installation of the bulb.
The P21W is a single-filament bulb rated at 21 watts, dedicated solely to turn signal output at the rear of the vehicle.
The P21W uses a BA15s bayonet base, which is a single-contact base with symmetrically placed pins. This base is not interchangeable with the BAY15d base found on the P21/5W, as the pin configurations differ between the two.
The front turn signal position on the Mercedes-Benz 450SLC requires the P21/5W across all model years from 1973-1980, indicating no variation in front bulb specification throughout the entire production run covered by these records.
The rear turn signal position specifies the P21W across all model years from 1973-1980, reflecting the same consistency seen in the front position.
Because the P21/5W and P21W use different base types, the two bulbs are not interchangeable with each other, and substituting one for the other in either position is not possible without modification to the socket.