Mercedes-Benz C240 front side marker bulbs use 12961 size while rear side marker bulbs use 12821 size. The replacement chart covers 2001 through 2005 production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz C240 uses the T10 miniature wedge bulb form factor for both front and rear side markers across the 2001-2005 model years.
The T10 designation refers to a tubular bulb with a width of 10 millimeters, commonly used in low-intensity automotive lighting positions such as side markers.
Both marker positions share the W2.1x9.5d base type, a wedge-style base where the electrical contacts are formed by the glass envelope itself rather than a separate metal cap.
The front side marker uses Philips part number 12961, rated at 12 volts and 5 watts.
The rear side marker uses Philips part number 12821, also rated at 12 volts and 5 watts.
Although the 12961 and 12821 share identical electrical ratings and the same T10 wedge base, they carry distinct Philips part numbers, which indicates a fitment distinction between the two positions despite their physical and electrical similarities.
The 5-watt rating places both bulbs in the low-wattage category typical of marker and courtesy lighting, as opposed to higher-wattage bulbs used in headlamp or brake lamp applications.
The W2.1x9.5d base specification denotes a wedge base with a width of 2.1 millimeters and a length of 9.5 millimeters, a standardized format shared across many automotive manufacturers.