The Mercedes-Benz 300SD front side marker bulb size measures 1034 or P21/5W, while the rear side marker bulb size measures P21/4W, 3893, or 12821. The replacement chart contains bulb size specifications across 1978 to 1993 vehicle production years.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz 300SD uses two distinct bulb standards across its model years: the ANSI standard, common in the US and Canada, and the ECE standard, used in Europe and worldwide markets.
The P21/5W is the most frequently specified bulb in these records, covering the front side marker position across the 1978-1985 model years. It is an ECE-standard dual-filament signalling bulb operating at 12V with a 21W and 5W output, mounted on a BAY15d bayonet base.
The 1034 bulb, specified for the front side marker on the 1992-1993 300SD, is an ANSI-standard dual-filament bulb also using a BAY15d bayonet base, rated at 12V and 21/5W. It is described as a variant of the 1157.
Because both the P21/5W and the 1034 share the BAY15d bayonet base and operate at the same 12V, 21/5W rating, their physical and electrical characteristics are closely related, though they originate from different standardization systems.
The rear side marker on the 1992-1993 300SD uses the P21/4W, an ECE-standard dual-filament bulb rated at 12V with a 21W and 4W output. Unlike the P21/5W, it uses a BAZ15d bayonet base, which is not interchangeable with the BAY15d base used in other positions.
The BAZ15d base of the P21/4W has an offset pin configuration that differs from the BAY15d, meaning substitution with P21/5W or 1034 bulbs is not physically compatible despite similar wattage ratings.
The 3893 bulb covers the rear side marker position on the 1981-1985 300SD. It is an ANSI-standard dual-filament bulb with a BAY15d bayonet base, rated at 12V, though its individual filament wattages are not specified in the provided data.
The rear side marker on the 1978-1980 300SD uses the 12821, a Philips part number designating a miniature wedge bulb of the T10 type with a W2.1x9.5d base, rated at 12V and 5W. As a single-filament wedge bulb, it is electrically and mechanically distinct from the dual-filament bayonet bulbs used in other positions and years.
The shift from the 12821 wedge bulb to the 3893 bayonet bulb in the rear side marker position between the 1980 and 1981 model years represents a change in both base type and filament configuration, making the two bulbs non-interchangeable.
Across all positions and years in these specifications, the 300SD draws from three different base types: BAY15d, BAZ15d, and W2.1x9.5d. Each base type is mechanically distinct, and bulbs from one base family cannot be fitted into sockets designed for another.