Freightliner Cascadia Turn Signal Bulb Size

Additional Notes

• The Freightliner Cascadia front turn signal uses two distinct bulb types across its production span, with the 4157NA specified for 2008-2017 and the 1156 specified for 2018-2022.
• The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and classified under the ANSI standard applicable in the United States and Canada.
• The 4157NA is a dual-filament bulb rated at 12V with a 27W/7W output split between its two filaments, housed in a T25 wedge form factor with natural amber glass, and also classified under the same ANSI standard.
• The natural amber glass of the 4157NA produces a yellow-orange light output without the use of a colored lens or coating, which distinguishes it from clear-glass variants in the same bulb family.
• The 1156 and 4157NA are not interchangeable. The 1156 uses a BA15s bayonet base, while the 4157NA uses a wedge base, making the two physically incompatible at the socket level.
• Beyond the base type, the filament count differs between the two bulbs. The 1156 carries a single filament, whereas the 4157NA carries two, meaning their electrical configurations serve different circuit requirements.
• The wattage also differs between the two types. The 1156 draws 21W on its single filament, while the 4157NA draws 27W on its primary filament and 7W on its secondary, resulting in a higher maximum load for the 4157NA.