The 2057 bulb is the most frequently specified size across both front and rear turn signal positions on the Peterbilt 224, appearing across model years 1987-1994.
The 2057 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with filaments drawing 26.9W and 8W respectively, making it suitable for combined stop and turn signal functions.
The 2057 is classified as a brighter variant of the 1157, meaning the two bulbs share the same base type but differ in light output and wattage.
The 198 bulb is a T5 miniature wedge type rated at 12V and 2W, a single-filament low-wattage bulb used in specific trim configurations of the Peterbilt 224.
Both the 2057 and 198 are ANSI-standardized bulbs recognized in the US and Canada, meaning their physical and electrical specifications conform to a defined industry standard.
The 198 and 2057 use fundamentally different base types, the former being a wedge and the latter a bayonet, making them physically non-interchangeable without a socket adapter.
On the Peterbilt 224, the 198 bulb is tied to specific headlamp configurations rather than serving as a general replacement, with front and rear fitment varying by whether the vehicle is equipped with 4 Round Headlamps or Halogen Capsule Headlamps.
In the 1989 front turn signal position, the 198 and 2057 assignments are reversed relative to most other years, with the 198 listed as the standard fitment and the 2057 specified only for the 4 Round Headlamps configuration.
The 1993 rear turn signal is the only position in the specifications where the Halogen Capsule Headlamp configuration is cited as a condition for the 198 bulb fitment.
Selecting the correct bulb for the Peterbilt 224 requires confirming the headlamp configuration of the specific vehicle, as the same model year can require either a 2057 or a 198 depending on that configuration.