The Mercedes-Benz CLK430 front side marker bulb uses 12961 or 12821 size, while the rear side marker bulb uses 12961 or P21/4W size. The replacement chart covers 1999 to 2003 vehicle production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz CLK430 front side marker uses two distinct bulb sizes across its model years, with the 12961 fitted in 1999 and 2003, and the 12821 fitted in 2000-2002.
Both the 12961 and 12821 are Philips part numbers designating miniature wedge bulbs of the T10 type, each operating at 12V and 5W with a W2.1x9.5d base.
Despite carrying different part numbers, the 12961 and 12821 share identical electrical ratings and the same W2.1x9.5d wedge base, which is a push-in base type requiring no rotation during installation.
The rear side marker for the CLK430 uses the P21/4W bulb in 1999-2002, while the 2003 model year transitions to the 12961.
The P21/4W is an ECE-standard bulb, meaning it conforms to European and international regulations for signalling lamps rather than SAE standards common in North American markets.
The P21/4W operates on a BAZ15d bayonet base, which is an offset twin-contact base. The offset pin spacing prevents incorrect insertion of a single-filament bulb in place of the dual-filament unit.
At 21W and 4W respectively, the P21/4W carries substantially higher wattage on its primary filament than the 5W T10 wedge bulbs used elsewhere in the CLK430 side marker positions.
The rear side marker position on the 2003 CLK430 uses the 12961, the same T10 wedge bulb as the front side marker that year, making the two positions interchangeable for that model year.
The BAZ15d base of the P21/4W is physically incompatible with the W2.1x9.5d wedge socket, meaning rear side marker bulbs from 1999-2002 cannot be substituted with the T10 wedge type without a socket adapter.