Mercedes-Benz S420 front fog lights utilize H1 and H3 bulb sizes, while rear fog lights require P21W bulbs. The replacement chart covers 1994 to 1999 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 front fog light on the Mercedes-Benz S420 uses the H1 bulb for model years 1995-1999, while the 1994 model year uses the H3 bulb instead. These two types are not interchangeable due to their different base designs, making year verification necessary before sourcing a replacement.
The H1 is a single-filament halogen bulb rated at 12V and 55W, built to the ECE standard with a P14.5s base. It holds approval across Europe, the US, and Japan.
The H3 is also a single-filament halogen bulb rated at 12V and 55W under the ECE standard, but it uses a PK22s base rather than the P14.5s found on the H1. Despite sharing the same wattage and voltage rating, the differing base types make H1 and H3 bulbs physically incompatible with each other's housings.
The rear fog light on the S420 uses the P21W bulb across model years 1995-1999. The P21W is a single-filament signalling bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
The P21W operates at a significantly lower wattage than the H1 and H3 halogen bulbs used in the front fog positions. This reflects its role as a signalling bulb rather than an illumination source, where lower power output is standard for rear-facing signal applications.
All three bulb types specified for the S420, H1, H3, and P21W, conform to the ECE standard, which governs automotive lighting across Europe and much of the world, and each carries approval for use in the US and Japan as well.
The BA15s bayonet base of the P21W is a single-contact design, which is a common fitment in rear signalling applications. It differs structurally from the pin-type bases used by the H1 and H3, meaning no crossover fitment is possible between the front and rear fog light positions.