The Mercedes-Benz ML320 brake light uses a P21W bulb size for illumination. Available data covers the span from 1998 through 2003 and from 2007 through 2009.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21W is the sole bulb type specified across all brake lighting positions on the Mercedes-Benz ML320, covering both the standard brake lights and the center high mount stop light.
The P21W is an ECE-standard single-filament bulb rated at 12 volts and 21 watts, designed for signalling applications such as brake lights.
The P21W uses a BA15s bayonet base, which is a single-contact bayonet fitting. The "s" in BA15s denotes a single contact at the base, distinguishing it from dual-contact variants that are not interchangeable with it.
Because the BA15s base is single-contact, substituting a dual-contact bayonet bulb such as the BAY15d would result in an incompatible fitment, as the pin alignment and electrical contact configuration differ between the two base types.
The standard brake light specification covers model years 1998-2003 and 2007-2009, all calling for the P21W.
The center high mount stop light specification covers model years 1998-2003 and 2007, also using the P21W, making it electrically and physically consistent with the standard brake light positions across those years.
The ECE designation on the P21W indicates the bulb conforms to United Nations Economic Commission for Europe regulations, a standard widely adopted outside North America as well as in many global markets.
At 21 watts on a 12-volt system, the P21W draws approximately 1.75 amperes per bulb, a figure relevant when assessing circuit load in applications where multiple brake bulbs operate simultaneously.