The Mercedes-Benz S600 brake light utilizes P21/5W and P21/4W bulb sizes for the rear lighting system. Data for the specified components covers the period from 1994 through 1999.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz S600 brake light circuit relies on two distinct dual-filament bulb types across its model years: the P21/5W for 1996-1999 and the P21/4W for 1994.
The P21/5W operates at 12V with a 21W main filament and a 5W secondary filament, conforming to ECE standards applicable across European and worldwide markets.
The P21/4W shares the same 12V, 21W main filament rating as the P21/5W but carries a reduced 4W secondary filament, making the two bulbs functionally distinct despite their similar appearance.
A critical interchangeability warning applies to the 1994 Mercedes-Benz S600: the P21/4W uses a BAZ15d bayonet base, which differs from the BAY15d base of the P21/5W used in later model years, meaning the two bulbs are not physically interchangeable.
The BAZ15d and BAY15d bases are offset-pin bayonet fittings designed to prevent incorrect installation, so a P21/5W cannot be seated into a socket intended for a P21/4W, and vice versa.
The center high mount stop light on the S600 for 1996-1999 uses the H21W, a single-filament bulb rated at 12V and 21W under ECE standards.
The H21W is fitted with a BAY9s base, a single-contact bayonet mount that is physically incompatible with the dual-contact BAY15d and BAZ15d bases used by the brake bulbs in the same vehicle.
Because the H21W is a single-filament bulb, it serves solely as a stop light signal source, without the combined tail and stop light function that the dual-filament P21/5W provides in the main brake assemblies.