The 2057 bulb is the most frequently specified size across both front and rear turn signal positions on the Peterbilt 376, appearing across model years 1988-1999.
The 2057 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with filaments drawing 26.9W and 8W respectively, and is recognized under ANSI standards in both the US and Canada.
As a dual-filament design, the 2057 supports two independent brightness levels within a single bulb, which is typical for combined stop and tail light functions in automotive applications.
The 2057 is described as a brighter variant of the 1157, meaning the two share the same BAY15d base type but differ in wattage output, making them physically interchangeable in some contexts though not electrically identical.
The 198 bulb is a miniature wedge type in the T5 form factor, rated at 12V and 2W, and also carries ANSI recognition for the US and Canadian markets.
The 198 is a single-filament, low-wattage wedge bulb, which is a fundamentally different construction from the dual-filament bayonet-base 2057, meaning the two are not interchangeable.
On the Peterbilt 376, the 198 bulb appears exclusively in the front turn signal position and is always tied to a specific headlamp configuration, such as 4 round headlamps, 4 rectangular headlamps, or halogen capsule headlamps.
The rear turn signal on the Peterbilt 376 uses the 2057 across all listed model years, with the sole exception of the 1994 model year fitted with 4 rectangular headlamps, which specifies the 198 instead.
Several model years list both the 2057 and the 198 for the front turn signal, with the correct fitment determined by the headlamp configuration present on the specific vehicle rather than the model year alone.
The headlamp configuration on a given Peterbilt 376 unit is therefore a critical factor in selecting the correct front turn signal bulb, and in at least one rear application as well.