The Mercedes-Benz GL320 front inner turn signal requires a 3457NA bulb size, while front turn signals use either 3457NA or 12961 bulbs, and rear turn signals require PY21W or 12496 bulbs. The replacement chart covers 2007 to 2009 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 3457NA is the most frequently specified bulb across the Mercedes-Benz GL320 turn signal positions, appearing in both the Front Inner Turn Signal and as the main Front Turn Signal bulb for all three model years covered.
The 3457NA is an ANSI-standard dual-filament wedge bulb rated at 12V with a 27W high filament and 7W low filament, housed in natural amber glass with a T25 body.
Its dual-filament design allows a single bulb to serve two lighting functions simultaneously, which is why it is suited to positions where both turn signal and parking light duties are combined.
The natural amber glass of the 3457NA produces amber light without relying on a colored lens, distinguishing it from clear-glass variants in the same bulb family.
The side rearview mirror turn signal on the Mercedes-Benz GL320 uses the 12961 for all three model years, a miniature T10 wedge bulb with a W2.1x9.5d base rated at 12V and 5W.
The T10 form factor of the 12961 is physically smaller than the T25 body of the 3457NA, meaning the two bulb types are not interchangeable despite sharing the same 12V operating voltage.
The rear turn signal position does not use a consistent bulb type across all model years; the 2007 and 2009 model years specify the PY21W, while the 2008 model year specifies the 12496.
The PY21W is an ECE-standard single-filament amber bulb rated at 12V and 21W, fitted with a BAU15s offset bayonet base, which physically prevents substitution with standard BA15s-based bulbs.
The BAU15s base of the PY21W has an offset pin arrangement specifically designed to prevent incorrect installation of non-amber bulbs in turn signal sockets, a feature built into the ECE regulatory framework.
The 12496 is a Philips/Osram halogen bulb rated at 12V; its specification for the 2008 rear turn signal position indicates that the 2008 model year rear housing may not be directly compatible with the PY21W used in 2007 and 2009.