The Mercedes-Benz CLK320 tail light requires P21/4W and 12821 bulb sizes for the rear lighting assembly. Data for the specified components covers the period from 1998 through 2005.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz CLK320 outer tail light uses two distinct bulb types across its model years: the P21/4W and the T10 wedge format, represented by Philips part numbers 12961 and 12821.
The P21/4W is an ECE-standard dual-filament bulb rated at 12V with a 21W main filament and a 4W secondary filament, mounted on a BAZ15d bayonet base. Its dual-filament design allows a single bulb to serve two lighting functions simultaneously.
Both the 12961 and 12821 are Philips part numbers for T10 miniature wedge bulbs sharing the same W2.1x9.5d base and identical electrical ratings of 12V at 5W.
For the CLK320 outer tail light in 2002-2005, the P21/4W is the specified bulb size for one of the two socket positions.
For model years 1998-2001, the outer tail light in one socket position specifies the 12961, a T10 wedge bulb, rather than the P21/4W.
The second socket position within the outer tail light shows variation across model years, with the 12821 specified for 1999, 2001, and 2002, while the P21/4W is specified for 1998, 2000, and 2003-2005.
Because the P21/4W uses a BAZ15d bayonet base and the T10 wedge bulbs use a W2.1x9.5d base, these two bulb types are not physically interchangeable despite occupying positions within the same tail light assembly.
Although the 12961 and 12821 share the same base type, voltage, and wattage, they carry different Philips part numbers, and substituting one for the other without confirming manufacturer fitment data is not advisable.