The Mercedes-Benz S350 tail light utilizes bulb sizes P21/4W and 12821 according to the provided data. Information for the specified components covers the range from 1994 through 2006.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz S350 outer tail light specifications reference three distinct bulb types across the listed model years: P21/4W, P21/5W, and 12821.
The P21/4W is an ECE-standard dual-filament signalling bulb rated at 12V with a 21W main filament and a 4W secondary filament, fitted with a BAZ15d bayonet base.
The P21/5W shares the same ECE-standard dual-filament construction and 12V/21W rating but carries a 5W secondary filament and uses a BAY15d bayonet base, making it physically incompatible with the P21/4W despite their similar designations.
The BAZ15d and BAY15d bases differ in pin offset geometry, meaning P21/4W and P21/5W bulbs are not interchangeable even though both are dual-filament bayonet types.
The 2006 S350 outer tail light position uses the P21/4W bulb across two separate sub-part entries within the specifications.
The 1995 S350 outer tail light specifications list both the P21/5W and the 12821 bulb, indicating that two different positions within the outer tail light assembly require different bulb types for that model year.
The 12821 is a Philips part number designating a miniature wedge-style T10 bulb with a W2.1x9.5d base, rated at 12V and 5W, functioning as a single-filament low-wattage lamp.
The 1994 S350 outer tail light also uses the 12821 bulb, consistent with the 1995 specification for that position.
The W2.1x9.5d wedge base of the 12821 is a push-fit type with no bayonet locking mechanism, distinguishing it entirely from the BAZ15d and BAY15d bases used by the P21/4W and P21/5W bulbs.
The P21/4W and P21/5W carry ECE recognition, indicating their design and output conform to European and international lighting regulations for signalling applications.