The Mercedes-Benz SL320 tail light requires a P21/4W bulb size for proper installation and function within the rear lighting assembly. Data for the specified component covers the range from 1994 through 1997.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21/4W is the sole bulb type specified across all listed model years of the Mercedes-Benz SL320, appearing in both the outer tail light positions covered by the data.
The P21/4W is an ECE-standard dual-filament bulb, meaning it contains two separate filaments within a single glass envelope, each rated at a different wattage.
The two filaments operate at 21 watts and 4 watts respectively, with the higher-wattage filament typically serving the brake or turn signal function and the lower-wattage filament serving the running light function.
The bulb operates on a 12-volt electrical system, which is standard for passenger vehicles of this era.
The P21/4W uses a BAZ15d bayonet base, a fitting with two offset pins at unequal heights. This asymmetric pin arrangement is a deliberate design feature that prevents incorrect installation, as the bulb can only be seated in one orientation.
Because the BAZ15d base is offset, it is not interchangeable with the more common BA15d base, which has pins at equal heights, despite the two bases appearing visually similar.
The ECE designation indicates the bulb conforms to United Nations Economic Commission for Europe regulations, a standard adopted across European and many worldwide markets.
The 1995-1997 model years share an identical P21/4W specification for the outer tail light, indicating consistent fitment across that production span.