The Peterbilt 389 front turn signal bulb size measures 4157NA or 2057, while the rear turn signal bulb size measures 1157 or 2057. The replacement chart covers vehicle production years spanning 2008 to 2017 with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 4157NA and 1157 are the most widely used bulb types across the Peterbilt 389 turn signal specifications, with the 4157NA covering front turn signals for 2011-2017 and the 1157 covering rear turn signals for the same period.
The 4157NA is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and 7W low filament, conforming to ANSI standards applicable in both the United States and Canada.
The natural amber glass of the 4157NA produces a color-filtered output directly from the bulb itself, rather than relying on a colored lens housing to achieve the amber turn signal appearance.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W high filament and 5W low filament, also conforming to ANSI standards for the US and Canada.
The BAY15d bayonet base on the 1157 features two offset pins, which physically prevent incorrect insertion and ensure consistent filament alignment within the socket.
The 2057 shares the same BAY15d bayonet base as the 1157 and is rated at 12V with a 26.9W high filament and 8W low filament, making it the higher-output variant of the two bayonet-base bulbs listed.
Although the 2057 and 1157 share the same BAY15d base, their wattage ratings differ, and substituting one for the other may affect brightness output and compatibility with the vehicle's electrical load expectations.
The Peterbilt 389 (2008-2009) used the 2057 for both front and rear turn signals, while the 2011-2017 model years split the specification, using the 4157NA at the front and the 1157 at the rear.
The T25 wedge base of the 4157NA is physically incompatible with the BAY15d bayonet sockets used by the 1157 and 2057, meaning these bulb types are not interchangeable regardless of voltage or wattage similarities.
The high and low filaments across all three bulb types serve distinct functions, with the higher-wattage filament typically activating for turn signal or brake light operation and the lower-wattage filament serving as a running or parking light.