The Mercedes-Benz C280 tail light utilizes P21/5W, P21/4W, and 12821 bulb sizes depending on the specific version of the vehicle. Data for the bulb sizes covers the range from 1997 through 2007.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21/4W is an ECE-standard dual-filament signalling bulb rated at 12V with a 21W main filament and a 4W secondary filament. It uses a BAZ15d bayonet base, which is an offset-pin fitting designed to prevent incorrect installation.
The P21/5W shares the same ECE dual-filament signalling standard as the P21/4W but carries a slightly higher secondary filament rating of 5W rather than 4W. Its base type is BAY15d, which differs from the BAZ15d used by the P21/4W, making the two bulbs physically non-interchangeable despite their similar appearance.
The 12821 is a Philips part number designating a miniature wedge-type T10 bulb with a W2.1x9.5d base, rated at 12V and 5W. As a single-filament wedge bulb, it serves a fundamentally different electrical and mechanical role than the dual-filament bayonet types listed alongside it.
The Mercedes-Benz C280 inner tail light position uses the P21/4W across the 1994-1996 model years, indicating a consistent BAZ15d bayonet socket in that housing for that generation.
The outer tail light of the C280 transitions between bulb types across model years. The 1994-1996 outer tail light uses the 12821 wedge bulb, while the 2006-2007 outer tail light uses the P21/5W, reflecting a change in socket type between these generations.
The BAZ15d base of the P21/4W and the BAY15d base of the P21/5W differ in the positioning of their offset pins. Substituting one for the other is not possible without modifying the socket, as the pin offsets are specific to each base type.
The W2.1x9.5d base of the 12821 wedge bulb is a friction-fit wedge design with no pins or bayonet locking mechanism, contrasting with the twist-lock retention of the BAZ15d and BAY15d bases used by the P21/4W and P21/5W respectively.
Among the bulb types present in these specifications, the P21/5W appears exclusively in the 2006-2007 outer tail light position, while the P21/4W appears in both the inner tail light (1994-1996) and certain outer tail light years, making it the more broadly applied dual-filament type across the C280 range covered here.