The Peterbilt 377 front and rear turn signal bulbs utilize a 2057 or 198 size specification. The replacement chart covers vehicle production spanning 1987 to 2001.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 2057 bulb is the most frequently specified size across the Peterbilt 377 turn signal fitment data, appearing in both front and rear positions across the full 1987-2001 model year span covered by the specifications.
The 2057 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with filaments drawing 26.9W and 8W respectively, and it is classified as a brighter variant of the 1157 under the ANSI standard used in the US and Canada.
The 198 bulb is a miniature wedge type in the T5 form factor, rated at 12V and 2W, and is also an ANSI-standard part used in the US and Canadian markets.
The 198 bulb carries a significantly lower wattage than the 2057, and its single-filament, wedge-base construction makes the two bulbs physically and electrically incompatible with each other despite sharing the same 12V operating voltage.
On the Peterbilt 377, the 198 bulb is tied to specific headlamp configurations rather than serving as a general-fitment alternative, with conditions including "With 4 Rectangular Headlamps," "With 4 Round Headlamps," and "With Halogen Capsule Headlamps" noted across various model years.
The front turn signal on the 1994 Peterbilt 377 requires the 198 bulb specifically on units equipped with halogen capsule headlamps, while all other 1994 front turn signal applications use the 2057.
For the 1993 front turn signal, the 198 bulb applies to units with 4 rectangular headlamps, whereas the 2057 applies to other configurations in the same year.
The rear turn signal fitment for 1997 and 1995 model years includes the 198 bulb on units with halogen capsule headlamps alongside the standard 2057 fitment, indicating that headlamp type is a determining factor for bulb selection in those years.
The BAY15d bayonet base of the 2057 uses an offset pin arrangement to prevent incorrect installation, a design feature that distinguishes it from single-filament bayonet bulbs that share a similar outward profile.
Because the 198 and 2057 use entirely different base types, a wedge socket and a bayonet socket respectively, substitution between the two is not physically possible without modification to the socket housing.