Mercedes-Benz GL550 Turn Signal Bulb Size

Additional Notes

• The 3457NA bulb is the most frequently specified type across the Mercedes-Benz GL550 turn signal positions. It is a dual-filament T25 wedge bulb rated at 12V with a 27W main filament and a 7W secondary filament, finished in natural amber glass under the ANSI standard for the US and Canadian markets.
• The 3357NA bulb shares the same T25 wedge form and natural amber glass as the 3457NA but carries only a single filament rated at 27W. Despite their physical similarity, the two types are not interchangeable because the 3457NA provides a second low-wattage filament that the 3357NA does not.
• The front inner turn signal on the GL550 used the 3457NA for the 2008 and 2011-2012 model years, while the 2009-2010 model years required the single-filament 3357NA instead. This difference in filament count between otherwise similar-looking bulbs makes year-specific verification necessary for that position.
• The PY24WNA is specified for the front turn signal on the Mercedes-Benz GL550 from 2013-2016, but only on vehicles equipped with halogen capsule headlamps. It uses a PGU20-4 base and is rated at 12V and 24W. It is the ANSI amber variant of the ECE PY24W standard and is not a universal replacement for other amber bulb types due to its distinct base design.
• The side rearview mirror turn signal on the GL550 for the 2008-2010 model years used the 12961, a Philips-designated miniature T10 wedge bulb with a W2.1x9.5d base rated at 12V and 5W. Its low wattage and small form factor distinguish it from all other bulb types listed in these specifications.
• The rear turn signal shifted from the PY21W for 2008-2009 to the 12496 for 2010-2012. These two bulb types use different base designs, as the PY21W employs a BAU15s bayonet base while the 12496 is a specialty halogen type, making them physically incompatible with each other.
• The PY21W follows the ECE standard used in Europe and worldwide markets, whereas the 3457NA, 3357NA, and PY24WNA all follow the ANSI standard applicable to the US and Canadian markets. The presence of both standards within the same vehicle model across different years reflects regional regulatory differences in amber signaling requirements.
• The 12496 is identified by a Philips or Osram part number rather than an ANSI or ECE designation, placing it in a manufacturer-specific category. Its specification lists a 12V rating without a stated wattage, which sets it apart from every other bulb type in these specifications where wattage is explicitly noted.
• The BAU15s bayonet base on the PY21W is an offset-pin design, meaning the two pins are positioned asymmetrically to prevent incorrect installation. This base type is distinct from the wedge and PGU20-4 bases found on other bulbs in these specifications and is not physically compatible with standard single-contact bayonet sockets.
• Several positions on the GL550 require more than one bulb type within the same model year. The front turn signal for 2008-2010 lists both a main bulb and a separate side rearview mirror bulb, indicating that a single replacement part does not cover all turn signal functions for those years.