The Peterbilt 388 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 2015 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 Peterbilt 388 front turn signal uses the 4157NA bulb for model years 2011-2015. This is a dual-filament T25 wedge bulb rated at 12V with a high filament draw of 27W and a low filament draw of 7W.
The 4157NA features natural amber glass, meaning the bulb itself produces an amber color output without relying on a tinted lens to achieve the legally required turn signal color.
For model years 2008-2009, the Peterbilt 388 front turn signal uses the 2057 bulb instead of the 4157NA. These two bulbs are not interchangeable, as they use different base types: the 4157NA uses a wedge base while the 2057 uses a BAY15d bayonet base.
The 2057 bulb is a dual-filament type with a BAY15d bayonet base, rated at 12V with filament draws of 26.9W and 8W. It is described as a brighter variant of the 1157.
The rear turn signal on the Peterbilt 388 uses the 1157 bulb for model years 2011-2015, and the 2057 bulb for model years 2008-2009.
Both the 1157 and 2057 share the BAY15d bayonet base, which features two pins offset at different heights to prevent incorrect installation. Despite this shared base, the two bulbs differ in wattage output and are not rated as direct equivalents.
The 1157 operates at 12V with filament draws of 21W and 5W, making it notably lower in output than the 2057 at 26.9W and 8W on their respective filaments.
All three bulb types listed across these specifications conform to ANSI standards applicable in both the United States and Canada, indicating standardized electrical and physical tolerances across the range.
The dual-filament design present in all three bulbs allows a single socket to serve two lighting functions, typically combining turn signal operation on the high-wattage filament with a secondary function such as running or parking light on the low-wattage filament.
A fitment distinction exists between the front and rear turn signal positions for the 2011-2015 Peterbilt 388: the front position requires the 4157NA wedge-base bulb, while the rear position requires the 1157 bayonet-base bulb. The two positions are not served by the same bulb during those years.