The Mercedes-Benz 420SEL uses a P21/5W bulb size for front side markers and a 3893 bulb size for rear side markers. The replacement chart covers 1986 to 1991 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 420SEL uses two distinct bulb types across its front and rear side marker positions for the 1986-1991 model years: the P21/5W at the front and the 3893 at the rear.
The P21/5W is an ECE-standard dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The BAY15d bayonet base features two offset pins that prevent incorrect insertion, a design shared by both the P21/5W and the 3893 despite their differing standards of origin.
The 3893 follows the ANSI standard used in the United States and Canada, classifying it as a North American specialty application bulb operating at 12V with a dual-filament configuration.
Although both bulbs share the BAY15d base type, the P21/5W and 3893 are governed by different regulatory standards, ECE and ANSI respectively, which affects their rated output specifications and regional certification.
The front side marker position on the 420SEL uses the P21/5W exclusively across all six model years covered, indicating a consistent European-specification fitment for that position.
The rear side marker position uses the 3893 across all six model years, reflecting a North American-specification fitment distinct from the front marker's European-standard bulb.
The dual-filament nature of both bulbs means each contains two separate tungsten filaments within a single envelope, allowing the bulb to serve more than one lighting function from a single socket.
Because the P21/5W and 3893 carry different wattage ratings and certification standards, substituting one for the other in either marker position is not supported by these specifications.