The Mercedes-Benz E420 front side marker bulb uses a 12961 size with P21/5W designation, while the rear side marker bulb utilizes 12821, 232, or 5008 sizes. The replacement chart covers 1994 to 1997 model 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 E420 uses different front side marker bulbs across its model years, with the 1994 and 1995 model years specifying the P21/5W and the 1997 model year specifying the 12961.
The P21/5W is an ECE-standard dual-filament signalling bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. Its dual-filament design distinguishes it from the single-filament bulbs found elsewhere in the E420 specifications.
The 12961 is a Philips part number for a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W. The same base type and ratings apply to the 12821, which is specified for the rear side marker position in the 1997 model year.
Because the 12961 and 12821 share identical base types, voltage ratings, and wattage, they are physically interchangeable in terms of socket fitment, though they carry distinct Philips part numbers assigned to different positions on the vehicle.
The rear side marker position shows three different bulb types across the three listed model years, with the 1994 E420 specifying the 5008, the 1995 specifying the 232, and the 1997 specifying the 12821.
The 232 is an ANSI-standard festoon bulb with an SV8.5 base, rated at 12V and 3W. Festoon bulbs are cylindrical in form and seat by contact pressure at each end rather than by a bayonet or wedge mechanism, making them incompatible with socket types designed for wedge or bayonet bases.
The 5008 is an ANSI-standard single-filament bulb with a BA15s bayonet base, rated at 12V and described as a lower wattage variant of the 1156. The BA15s base uses a single contact pin, which is not interchangeable with the BAY15d base used by the P21/5W despite both being bayonet-type fittings.
The BAY15d base of the P21/5W features two offset pins to enforce correct polarity orientation for its dual-filament circuit, whereas the BA15s base of the 5008 uses a single pin. This structural difference means the two bulb types cannot be substituted for one another even if wattage were comparable.
The T10 wedge bulbs specified for the 1997 model year, the 12961 at the front and the 12821 at the rear, operate at a lower wattage than the P21/5W specified for the front position in 1994-1995, reflecting a difference in the light output and circuit design between those model years.
The ANSI and ECE standards referenced in the specifications represent distinct regional classification systems. ANSI designations such as 232 and 5008 are primarily used in North American markets, while ECE designations such as P21/5W are used in European and international markets.