The Mercedes-Benz S420 tail light utilizes bulb size 12821 and bulb size P21/5W according to the provided specifications. Data for the tail light covers the range from 1994 to 1999.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The outer tail light of the Mercedes-Benz S420 uses three distinct bulb types across its production years: the Philips 12961, the Philips 12821, and the ECE-standard P21/5W.
Both the 12961 and 12821 are Philips part numbers for miniature wedge bulbs of the T10 type, each rated at 12V and 5W with a W2.1x9.5d base.
Although the 12961 and 12821 share identical electrical ratings and base types, they carry different Philips part numbers and are listed as separate fitments across different positions in the outer tail light assembly.
The P21/5W is an ECE-standard dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W main filament and a 5W secondary filament, making it electrically and physically incompatible with the single-filament T10 wedge bulbs used in other positions.
The BAY15d base of the P21/5W is an offset twin-contact bayonet fitting, a design that prevents incorrect installation by ensuring the two filaments are oriented to their correct circuits.
For the 1996 model year, the Mercedes-Benz S420 outer tail light specifies the P21/5W for both listed positions, representing the only year in which that bulb type appears across multiple slots simultaneously.
The 1997-1999 outer tail light assembly uses the Philips 12961 in one position and the Philips 12821 in another, indicating that two different T10 wedge bulbs serve separate functions within the same unit.
The 1995 model year outer tail light uses the P21/5W in one position and the Philips 12821 in the other, combining a dual-filament bayonet bulb with a single-filament wedge bulb within the same assembly.