The 2057 is an ANSI-standard dual-filament bulb with a BAY15d bayonet base, rated at 12V with a high filament draw of 26.9W and a low filament draw of 8W. Its dual-filament design allows it to serve both turn signal and running light functions from a single socket.
The 2057 is a brighter variant of the 1157, meaning the two share the same BAY15d base type but differ in output. This distinction is relevant to fitment, as the higher wattage of the 2057 may affect compatibility with sockets or circuits designed around the 1157.
The 198 is an ANSI-standard miniature wedge bulb in a T5 form factor, rated at 12V and 2W. Its single-filament, low-wattage design contrasts sharply with the 2057 and reflects a different application role within the turn signal system.
The 2057 is the dominant bulb across the Peterbilt 353 turn signal specifications, appearing in both the front and rear positions for the 1986-1988 model years.
On the 1988 Peterbilt 353, the front turn signal uses the 198 bulb specifically in configurations with 4 round headlamps, while the 2057 applies to other configurations. This indicates that headlamp style directly determines front turn signal bulb fitment for that year.
The 1987 Peterbilt 353 front turn signal similarly splits between the 198 and 2057 based on headlamp configuration, with the 198 specified for vehicles equipped with 4 rectangular headlamps.
The 198 bulb appears in the rear turn signal position for the 1986 Peterbilt 353 only in configurations with halogen capsule headlamps, establishing another instance where headlamp type governs bulb selection outside of the headlamp circuit itself.
The BAY15d bayonet base of the 2057 uses offset pins to prevent incorrect insertion, a design feature that distinguishes it from single-filament bayonet bases and prevents substitution with incompatible single-filament bulbs.
The T5 wedge form factor of the 198 bulb is retained directly by the socket without a separate base locking mechanism, relying on the wedge shape of the glass envelope to maintain contact with the socket terminals.
Because the 198 and 2057 use physically incompatible base types, a wedge socket and a BAY15d bayonet socket are not interchangeable, making headlamp configuration a critical factor when sourcing the correct front or rear turn signal bulb for the 353.