The Mercedes-Benz S320 front fog light utilizes H1 and H3 bulb sizes, while the rear fog light requires a P21W size bulb. The replacement chart covers vehicle production spanning 1994 to 1999 with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The front fog light on the Mercedes-Benz S320 uses the H1 bulb for model years 1995-1999, while the 1994 model year uses the H3 bulb instead. These two bulb types are not interchangeable despite sharing identical wattage ratings, as they use different base fittings.
The H1 bulb operates on a P14.5s pin base, whereas the H3 bulb uses a PK22s base. The physical difference in base design means a socket built for one will not accept the other.
Both the H1 and H3 are single-filament halogen bulbs rated at 12V and 55W. The single-filament design means each bulb serves one lighting function only, with no secondary filament for an alternate mode.
Both H1 and H3 bulbs conform to ECE standards, making them approved for use in Europe, the United States, and Japan. This international approval reflects a standardized output and construction specification.
The rear fog light on the S320 uses the P21W bulb across model years 1995-1999. The P21W is a single-filament signalling bulb rated at 12V and 21W, a notably lower wattage than the halogen fog bulbs used at the front.
The P21W uses a BA15s bayonet base, which is a single-contact bayonet fitting. This base type is mechanically distinct from the pin bases found on the H1 and H3, making cross-position substitution physically impossible.
The P21W also carries ECE certification for use across Europe and worldwide markets. Its classification as a signalling bulb reflects its role in rear visibility rather than forward illumination.
The front fog position on the 1994 S320 is the only position across all listed years and sub-parts that calls for an H3 bulb. All other front fog positions in the dataset specify H1.