Freightliner Argosy Turn Signal Bulb Size

Additional Notes

• The Freightliner Argosy front turn signal specifications cover the 2005-2007 model years, with two distinct bulb types listed across that range.
• The 4157NA is the bulb type specified for the 2005-2006 model years. It is an ANSI-standardized dual-filament wedge bulb in the T25 form factor, rated at 12V with a 27W main filament and a 7W secondary filament, and it produces its amber output through natural amber glass rather than a coating.
• The 5702AK is specified for the 2007 model year. It is a Sylvania part number designating a coated variant of the ANSI 3157 bulb, sharing the same T25 wedge form factor and 12V, 27W/7W electrical ratings as the 4157NA, but achieving its amber output through an applied coating over clear glass rather than through the glass itself.
• Although the 4157NA and 5702AK share the same T25 wedge base, voltage, and wattage ratings, they are not the same part. The 4157NA is an ANSI-standardized type recognized across the US and Canadian markets, while the 5702AK is a manufacturer-specific part number tied to Sylvania.
• The dual-filament design present in both bulb types means each bulb serves two functions within a single housing, with the higher-wattage filament (27W) typically handling the turn signal flash and the lower-wattage filament (7W) handling a secondary function such as parking or running light duty.
• The amber color output method differs between the two specified bulbs. Natural amber glass, as used in the 4157NA, is inherent to the glass envelope itself, while the amber coating on the 5702AK is an external application. This distinction can affect light transmission characteristics even when wattage ratings are identical.