The Mercedes-Benz E420 brake light uses bulb sizes P21/4W and P21W according to the provided data. The information covers a range of years starting from 1994 and ending in 1997.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz E420 uses two distinct bulb types across its brake light positions: the P21W and the P21/4W, both governed by ECE standards recognized in Europe and worldwide.
The P21W is a single-filament signalling bulb operating at 12V with a 21W output and a BA15s bayonet base, meaning it carries current through a single tungsten filament.
The P21/4W is a dual-filament signalling bulb operating at 12V with filaments rated at 21W and 4W respectively, fitted with a BAZ15d bayonet base, which physically differs from the BA15s base used by the P21W.
The BAZ15d base of the P21/4W and the BA15s base of the P21W are not interchangeable, as the offset pin configuration of the BAZ15d is designed to prevent incorrect single-filament bulb installation in a dual-filament socket.
For the 1997 Mercedes-Benz E420, the brake light position specifies the P21/4W, while the 1994 and 1995 model years specify the P21W for that same position, indicating a base and filament configuration change between those years.
The Center High Mount Stop Light on the E420 uses the P21W across the 1994-1997 model years covered in the specifications, with a BA15s bayonet base and a single 21W filament at 12V.
Because the brake light socket for the 1997 model accepts a BAZ15d base, substituting a BA15s bulb such as the P21W in that position would constitute an incorrect fitment regardless of wattage similarity.