International TerraStar front turn signal uses 3157NA bulb size and rear turn signal uses 1157 bulb size. Replacement chart covers 2010 to 2018 production years with bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The International TerraStar uses the 3157NA bulb for the front turn signal across all model years from 2010-2018.
The 3157NA is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and 7W low filament, constructed with natural amber glass that produces an amber color output without the need for an amber lens.
The "NA" suffix in the 3157NA designation specifically denotes the natural amber glass envelope, which distinguishes it from the clear-glass 3157 variant. Substituting a clear 3157 in place of a 3157NA would alter the color output at the front turn signal position.
The rear turn signal on the International TerraStar uses the 1157 bulb across all model years from 2010-2018.
The 1157 is a dual-filament bulb rated at 12V with a 21W high filament and 5W low filament, mounted on a BAY15d bayonet base. The BAY15d base features two offset pins that prevent incorrect insertion orientation.
Both the 3157NA and 1157 conform to ANSI standards applicable in the United States and Canada, indicating standardized electrical and physical specifications within those markets.
The front and rear turn signal positions on the TerraStar use different bulb types and base configurations, meaning the two bulbs are not interchangeable with each other despite both being dual-filament 12V units.
The dual-filament design of both bulbs allows a single housing to serve more than one lighting function, with the higher-wattage filament typically assigned to the active turn signal flash and the lower-wattage filament to a secondary function such as a parking or running light.