The Mercedes-Benz CL600 tail light utilizes 12821 and P21/4W bulb sizes for the rear illumination system. Data for the specified lighting components covers the period from 1998 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 CL600 outer tail light uses two distinct bulb types across its model years: the P21/4W and the T10 wedge type, each serving different functions within the same light assembly position.
The P21/4W is an ECE-standard dual-filament signalling bulb rated at 12V with a 21W/4W output split, mounted on a BAZ15d bayonet base. The dual-filament design allows it to serve two lighting functions simultaneously, such as running light and brake or turn signal duties, within a single bulb.
The BAZ15d bayonet base on the P21/4W is an offset pin design, meaning the two pins are positioned at different heights around the base. This prevents incorrect insertion and ensures the filaments align with their intended optical positions inside the housing.
The CL600 outer tail light uses the P21/4W across the 1998-1999 and 2001-2004 model years.
Bulb numbers 12961 and 12821 are both Philips manufacturer part numbers referring to T10 miniature wedge bulbs. Both share the same W2.1x9.5d base type and the same 12V, 5W electrical rating.
The W2.1x9.5d base is a wedge-style base where the glass envelope itself acts as the retaining mechanism, with no separate metal base or pins. The numeric portion of the designation refers to the contact width and insertion depth.
The 12961 and 12821 T10 bulbs appear in the outer tail light position for the 1998-1999 and 2005-2006 model years respectively, operating alongside the P21/4W in the same assembly across overlapping years.
Because the P21/4W uses a BAZ15d bayonet base and the T10 uses a wedge base, the two bulb types are not interchangeable with each other, despite occupying positions within the same outer tail light assembly.
The 12961 and 12821 Philips part numbers, while technically identical in base type and electrical rating, are distinct catalog entries and may differ in filament construction, glass envelope coating, or certification batch, making cross-substitution dependent on Philips compatibility documentation rather than specification alone.