The BMW M3 tail light utilizes bulb sizes P21W, P21/4W, P21/5W, and 12821 depending on the specific version required for the lighting assembly. Data for the lighting components covers the range from 1988 through 2011.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21/4W is the most frequently specified bulb across the BMW M3 tail light data. It is a dual-filament ECE-standard signalling bulb rated at 12V with a 21W main filament and a 4W secondary filament, mounted on a BAZ15d bayonet base.
The BAZ15d base used by the P21/4W is offset-pin, meaning the two pins sit at different heights on the base. This prevents incorrect insertion and ensures the bulb is seated in the correct orientation for its dual-filament function.
The P21/5W shares a similar dual-filament design with the P21/4W but uses a BAY15d base instead of a BAZ15d base. Although both are dual-filament bayonet bulbs, their bases are not interchangeable.
The P21W is a single-filament bulb with a BA15s base rated at 12V and 21W. Its base differs from both the P21/4W and P21/5W, and it is not a drop-in substitute for either dual-filament type.
The 12821 is a Philips part number designation for a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W. Its wedge base format is physically distinct from the bayonet bases used by the P21-series bulbs.
For the BMW M3, the outer tail light on the 2011 model year uses a P21W, while the 2001-2006 model years use a P21/4W. These two bulbs differ in both filament count and base type, making them non-interchangeable.
The 1995-1999 outer tail light position lists the P21/4W, while a separate set of entries for overlapping years such as 1995-1996 also lists the P21/4W, and 1997-1998 lists the P21/5W. This indicates that different tail light assemblies or sub-positions within the same model year may require different bulb types.
The 1988-1991 and 1999 model years share the 12821 bulb in one of the listed positions. At 5W, this bulb operates at a significantly lower wattage than the P21-series bulbs, reflecting its use in a lower-intensity lighting function.