The Mercedes-Benz S500 tail light utilizes P21/4W and 12821 bulb sizes according to the provided specifications for the lighting components. Data for the specific bulbs 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 P21/4W is the most frequently specified bulb across the outer tail light positions of the Mercedes-Benz S500, covering model years 2000-2006 in both positions and also appearing in 1994 and 1999 in select fitments.
The P21/4W is a dual-filament ECE-standard bulb rated at 12V with a 21W main filament and a 4W secondary filament, mounted on a BAZ15d bayonet base.
The P21/5W shares the same ECE dual-filament design as the P21/4W but uses a BAY15d bayonet base instead of a BAZ15d base, making the two bulbs physically non-interchangeable despite their similar wattage ratings.
For the 1997-1999 model years, the Mercedes-Benz S500 outer tail light specifies the P21/5W exclusively for vehicles with special protection, with fitment restricted to vehicles within the ID range A 159651 through A 192207 and from ID A 192209 onward.
The Philips part numbers 12961 and 12821 both refer to miniature wedge bulbs of the T10 type, each rated at 12V and 5W, sharing the same W2.1x9.5d wedge base.
The 12961 appears in the specifications for the 1997 model year in one outer tail light position, while the 12821 covers the 1996-1999 model years in the second outer tail light position, indicating that both T10 wedge types serve distinct socket locations rather than the same one.
Because the P21/4W and P21/5W use different bayonet base configurations, BAZ15d and BAY15d respectively, substituting one for the other in S500 fitments where special protection variants are a factor would result in an incorrect physical fit.