The Mercedes-Benz ML550 front fog light requires an H7 bulb size, while rear fog lights use 921 or P21W bulb sizes. The replacement chart covers 2008 to 2011 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 ML550 uses the H7 bulb across all four model years (2008-2011) for the front fog light position.
The H7 is a single-filament halogen bulb operating at 12V and 55W, fitted with a PX26d base and rated under the ECE standard, which applies across Europe and worldwide markets, with additional approval in the US and Japan.
The PX26d base is a locking pin-type connector, meaning H7 bulbs are not interchangeable with wedge-base or bayonet-base bulb types without a socket adapter.
The rear fog light position on the ML550 uses two different bulb types depending on the model year, with the 2008 model year specifying the P21W and the 2009-2011 model years specifying the 921.
The P21W is an ECE-standard single-filament signalling bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
The 921 is an ANSI-standard wedge bulb of the T15 form factor, rated at 12V and 16W, and is the North American market counterpart commonly used in rear lighting positions.
The P21W and 921 are not directly interchangeable due to their differing base types: the P21W uses a BA15s bayonet fitting, while the 921 uses a wedge-style base.
The wattage difference between the P21W (21W) and the 921 (16W) in the rear fog light position reflects a specification change between the 2008 model year and the 2009-2011 model years.