The Mercedes-Benz ML550 front turn signal requires a PY24WNA or 3457NA bulb size, while the rear turn signal uses a PY21W or 12496 bulb size. The replacement chart covers 2008 to 2014 model 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 PY24WNA is an ANSI-standard amber bulb rated at 12V and 24W, fitted with a PGU20-4 base. It serves as the North American equivalent of the ECE PY24W and is specified for the front turn signal on the Mercedes-Benz ML550 for model years 2012-2014, exclusively on vehicles equipped with halogen capsule headlamps.
The 3457NA is an ANSI-standard dual-filament bulb in a T25 wedge form, with natural amber glass and a 12V rating. Its filaments operate at 27W and 7W respectively, making it capable of serving both a primary and a secondary lighting function within a single housing.
The 3457NA is specified for the ML550 front turn signal position for model years 2008-2011, representing the earlier generation fitment before the PY24WNA was introduced for the halogen capsule headlamp configuration.
The PY21W follows the ECE standard rather than the ANSI standard. It is a single-filament amber bulb rated at 12V and 21W, using a BAU15s offset bayonet base. The offset pin arrangement of the BAU15s base physically prevents incorrect installation of non-amber bulbs in the same socket.
The rear turn signal position on the ML550 alternates between two different bulb types across model years. The PY21W is specified for 2009 and 2011, while the 12496 is specified for 2008 and 2010.
The 12496 is a Philips and Osram part number designation for a 12V halogen bulb intended for specialty automotive applications. Unlike the other bulbs in these specifications, it is identified by a manufacturer part number rather than an ANSI or ECE standard designation.
The PY24WNA and the PY21W are not interchangeable. Beyond their wattage difference of 24W versus 21W, they use entirely different base types, the PGU20-4 and the BAU15s respectively, which prevents cross-installation between front and rear positions.
The 3457NA and the PY24WNA both occupy the front turn signal position across different ML550 model years, but they are not interchangeable. The 3457NA is a dual-filament wedge bulb while the PY24WNA is a single-filament bulb with a PGU20-4 base, and their sockets are physically incompatible.
The front turn signal specification for 2012-2014 includes a conditional note tied to the halogen capsule headlamp configuration, indicating that headlamp type is a relevant factor in determining the correct front turn signal bulb for those model years.