The Peterbilt 265 front and rear turn signals draw from two distinct ANSI-standard bulb types across the 1988-1994 model years: the 2057 and the 198.
The 2057 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a wattage split of 26.9W on the high filament and 8W on the low filament, making it suitable for combined stop and turn signal functions.
The 198 is a miniature wedge bulb in a T5 form factor, rated at 12V and 2W, representing a significantly lower output than the 2057.
The 2057 is noted as a brighter variant of the 1157, sharing the same BAY15d bayonet base, which means the two types are physically interchangeable in base fitment, though output levels differ.
On the Peterbilt 265, the 1992 front turn signal position lists both the 2057 and the 198, with the 198 applying specifically to trucks equipped with four round headlamps, indicating that headlamp configuration determines bulb fitment for that year.
The same headlamp-based split applies to the 1989 front turn signal, where the 198 is specified for the four round headlamp configuration while the 2057 covers the standard fitment.
The 1988 front turn signal specifies the 2057 explicitly for trucks with four rectangular headlamps, while the 198 applies to the remaining configuration, reinforcing that headlamp style is a critical fitment variable for this model.
The 1991 front turn signal lists only the 198, with no conditional qualifier, distinguishing it from adjacent years where dual fitment options are present.
The rear turn signal position uses the 2057 consistently across 1988-1994, with the sole exception being the 1989 model year when equipped with four round headlamps, which takes the 198 instead.
Because the 2057 and 198 differ in base type, wattage, and filament count, the two bulbs are not interchangeable, and headlamp configuration must be confirmed before selecting a replacement for either the front or rear turn signal position.