Mercedes-Benz C300 Turn Signal Bulb Size

Additional Notes

• The front turn signal on the Mercedes-Benz C300 uses two distinct bulb types across its model years, with the 12174NA fitted to 2015-2019 models equipped with halogen capsule headlamps and the PY24WNA fitted to 2011-2014 models with the same headlamp configuration.
• The 12174NA is an OEM-designated natural amber glass halogen bulb rated at 12V, meaning its amber color is produced by the glass coating rather than a colored lens or plastic housing.
• The PY24WNA is the North American ANSI-compliant amber variant of the ECE PY24W standard, rated at 12V and 24W, and uses a PGU20-4 base, which is a proprietary pin configuration not shared with common wedge or bayonet base types.
• The 2009-2010 front turn signal position uses the 3457NA, a dual-filament T25 wedge bulb rated at 12V with a 27W main filament and a 7W secondary filament, indicating it serves a combined signaling function at that position.
• The 2008 front turn signal uses the 3357NA, a single-filament T25 wedge bulb rated at 12V and 27W. Although the 3357NA and 3457NA share the same T25 form factor and wattage on their primary filament, the 3457NA carries an additional filament, making the two non-interchangeable without circuit consideration.
• The rear turn signal across multiple C300 model years alternates between the 12496 and PY21W, with the 12496 appearing in 2009, 2016-2017, and 2019, and the PY21W appearing in 2008, 2010-2011, 2015, and 2018.
• The PY21W follows the ECE international standard and uses a BAU15s offset bayonet base rated at 12V and 21W. The offset pin configuration of the BAU15s base prevents installation of non-amber standard BA15s bulbs, serving as a physical interchangeability safeguard.
• The 12496 is a Philips/Osram proprietary part number for a 12V specialty halogen bulb. Because it is identified by a manufacturer part number rather than an ANSI or ECE standard designation, direct substitution with standardized bulb types requires verification of base type and wattage compatibility.
• The "NA" suffix present on the 12174NA, PY24WNA, 3457NA, and 3357NA designations indicates North American market variants, typically distinguished by natural amber glass construction to satisfy SAE and DOT amber color requirements without relying on a tinted lens.
• The halogen capsule headlamp fitment note attached to the front and rear turn signal entries for 2011-2019 indicates that the listed bulb sizes apply specifically to C300 vehicles built with that headlamp configuration, and vehicles with a different headlamp type may require a different bulb specification.