Peterbilt 337 front turn signal bulbs use 3157NA size while rear turn signal bulbs use 1157 size. Replacement chart data covers 2010 through 2017 vehicle production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Peterbilt 337 uses two distinct bulb types across its turn signal positions: the 3157NA for the front and the 1157 for the rear, across the 2010-2017 model years.
Both the 3157NA and 1157 are ANSI-standardized bulbs rated for use in the United States and Canada, and both operate on a 12-volt electrical system.
Both bulb types feature dual-filament construction, meaning each bulb serves two brightness levels within a single housing, typically a higher-wattage filament for the turn signal function and a lower-wattage filament for a secondary function such as parking or running light duty.
The 3157NA, fitted in the front turn signal position of the Peterbilt 337, is a T25 wedge-type bulb rated at 27W on its primary filament and 7W on its secondary filament.
The "NA" suffix in the 3157NA designation indicates natural amber glass, meaning the bulb itself produces an amber-tinted output rather than relying on a colored lens to achieve the amber signal color.
The 1157, used in the rear turn signal position, draws 21W on its primary filament and 5W on its secondary filament, making it a lower overall wattage bulb than the 3157NA.
The 1157 uses a BAY15d bayonet base, a two-pin offset bayonet mount that is mechanically keyed to prevent incorrect insertion, distinguishing it from the wedge-style base of the 3157NA.
Because the 3157NA and 1157 use different base types, a wedge mount versus a bayonet mount, the two bulbs are not interchangeable between the front and rear turn signal sockets of the Peterbilt 337.