The Mercedes-Benz SL320 front fog light uses H1 and H3 bulb sizes, while the rear fog light requires a P21/4W bulb size. The replacement chart covers 1994 to 1997 production years 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 Mercedes-Benz SL320 front fog light uses the H1 bulb for the 1994-1995 and 1997 model years, while the 1996 model year uses the H3 bulb instead.
The H1 and H3 are not interchangeable despite sharing identical voltage and wattage ratings of 12V and 55W. Their base types differ, with the H1 using a P14.5s base and the H3 using a PK22s base, making socket compatibility the determining factor.
Both the H1 and H3 are single-filament halogen bulbs built to ECE standards, with approval also extended to the US and Japanese markets.
The rear fog light on the SL320 uses the P21/4W bulb for the 1995-1997 model years.
The P21/4W is a dual-filament signalling bulb rated at 12V with a split wattage of 21W and 4W across its two filaments, mounted on a BAZ15d bayonet base.
The BAZ15d base of the P21/4W features an offset pin arrangement, which physically prevents substitution with single-filament bayonet bulbs that share a similar appearance but use a different base configuration.
The front and rear fog light positions on the SL320 draw from entirely different bulb families, with halogen technology in the front and a signalling-type bulb in the rear.