Mercedes-Benz SLR McLaren front side marker bulb uses 12961 size while rear side marker bulb uses P21W size. The replacement chart covers vehicle production spanning 2005 to 2009.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz SLR McLaren uses two distinct bulb types across its side marker positions for the 2005-2009 model years: the 12961 at the front and the P21W at the rear.
The 12961 is a Philips part number designating a miniature wedge-style T10 bulb with a W2.1x9.5d base, rated at 12V and 5W.
The T10 wedge form factor is a small, pin-free bulb that is held in its socket by friction rather than a locking mechanism, which is characteristic of low-wattage marker and courtesy light applications.
The P21W follows the ECE (Economic Commission for Europe) naming standard, which is used in European and worldwide automotive lighting regulations, and carries a BA15s single-contact bayonet base rated at 12V and 21W.
The BA15s bayonet base uses a single contact point at its base, distinguishing it from the dual-contact BA15d variant. The two are not interchangeable despite sharing the same physical bayonet collar size.
The rear side marker draws significantly more wattage than the front, with the P21W rated at 21W compared to the 5W of the front 12961 bulb, reflecting the rear marker's role in signalling functions that require greater light output.
The W2.1x9.5d base designation on the 12961 specifies the wedge base width and pin spacing, and bulbs with differing base codes are not compatible with sockets designed for this specification.
The front side marker specification for the SLR McLaren remains consistent across the full 2005-2009 production span, with no variation in bulb size recorded across those model years.