Mercedes-Benz E550 Turn Signal Bulb Size

Additional Notes

• The Mercedes-Benz E550 front turn signal position uses three distinct bulb types across its model years: the 3457NA, 3357NA, and 2357NA, all of which conform to ANSI standards recognized in the United States and Canada.
• The 3457NA is a dual-filament T25 wedge bulb rated at 12V with a 27W primary filament and a 7W secondary filament. Its natural amber glass produces the required turn signal color without relying on a colored lens or socket filter.
• The 3357NA shares the same T25 wedge form factor and 12V/27W rating as the 3457NA but carries only a single filament, making the two bulbs physically similar yet functionally distinct. Substituting one for the other without confirming the circuit's filament requirements would result in incorrect operation.
• The 2357NA differs from both T25 wedge types by using a BAY15d bayonet base rather than a wedge mount. It is rated at 12V with a 26.9W primary filament and an 8W secondary filament. This base type is not physically interchangeable with the T25 wedge socket used by the 3457NA and 3357NA.
• The 2357NA was specified exclusively for the 2007 model year, while all subsequent years in the specifications use either the 3457NA or 3357NA, reflecting a socket-type change between the 2007 and 2008 production years.
• The 2013 Mercedes-Benz E550 is the only model year in the specifications that lists two different front turn signal bulbs for the same position, with the 3457NA assigned to vehicles equipped with the Traffic static LED headlamp and the 3357NA assigned to those without it. This makes headlamp configuration a determining factor in bulb selection for that year.
• For model years 2008-2012 and 2010-2012, the applicable bulb size is tied specifically to the Halogen Capsule Headlamp configuration, indicating that headlamp type influences front turn signal fitment across multiple years beyond 2013.
• The 3457NA is the specified bulb for the 2014-2016 model years without any conditional headlamp qualifier, suggesting a standardized fitment for those production years regardless of headlamp variant.
• Because the 3457NA and 3357NA share the same T25 wedge base, a single-filament 3357NA could physically seat in a socket designed for the dual-filament 3457NA. However, the missing second filament would leave one circuit non-functional, making the two types non-interchangeable in practice despite their physical similarity.
• The "NA" suffix present on all three bulb types in the specifications denotes natural amber glass, which is a factory-tinted envelope rather than a clear bulb used with an amber lens. This distinction affects color output and regulatory compliance for turn signal applications.