Mercedes-Benz ML450 front turn signal bulbs measure 3457NA size while rear turn signal bulbs measure PY21W size. The replacement chart covers 2010 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 ML450 uses two distinct turn signal bulb types across its front and rear positions for the 2010-2011 model years: the 3457NA at the front and the PY21W at the rear.
The 3457NA is an ANSI-standard bulb used in the United States and Canada. It follows the T25 wedge form factor and carries a dual-filament design rated at 12V with a 27W primary filament and a 7W secondary filament.
The dual-filament construction of the 3457NA means the bulb serves two electrical circuits within a single housing, a characteristic that distinguishes it from single-filament alternatives.
The natural amber glass of the 3457NA produces its amber signal color through the glass itself rather than through a colored lens or housing, which is reflected in the "NA" suffix of its designation.
The PY21W follows the ECE standard, which governs lighting regulations across Europe and many other markets worldwide. Its amber color is also produced by the glass of the bulb rather than an external lens.
The PY21W uses a BAU15s bayonet base, an offset single-pin fitting. The offset pin placement prevents the bulb from being seated in a socket intended for a standard BAY15s base, making the two types physically non-interchangeable.
The PY21W is a single-filament bulb rated at 12V and 21W, which places it in a different wattage and filament category than the 3457NA used at the front of the same vehicle.
Because the front and rear positions of the ML450 use bulbs from different international standards bodies, ANSI and ECE, the two bulb types are not interchangeable with each other despite both operating on 12V systems.