Peterbilt 320 Brake Bulb Size

Additional Notes

• The Peterbilt 320 brake bulb specifications cover model years 1987 through 2017, with three distinct bulb types appearing across that span: the 1157, the 2057, and the 198.
• The 1157 and 2057 are both dual-filament bulbs sharing the BAY15d bayonet base and a 12V operating voltage. The 2057 draws 26.9W on its high filament and 8W on its low filament, while the 1157 draws 21W and 5W respectively, making the 2057 the higher-wattage variant of the two.
• Despite their shared base type, the 1157 and 2057 are not interchangeable without consideration of wattage differences, as substituting one for the other affects light output and may affect circuit load.
• The Peterbilt 320 uses the 1157 bulb for brake applications in model years 2011-2017, representing a shift from the 2057 that preceded it.
• The 2057 bulb is specified for brake applications across model years 1987-2009, with some of those years also carrying a concurrent 198 fitment depending on headlamp configuration.
• The 198 is a miniature wedge bulb of the T5 type, rated at 12V and 2W, a single-filament design with no bayonet base, making it physically and electrically distinct from both the 1157 and 2057.
• The 198 bulb appears in the Peterbilt 320 brake specifications only under specific headlamp configuration conditions, including vehicles equipped with 4 round headlamps, 4 rectangular headlamps, or halogen capsule headlamps, across select years from 1987 through 1996.
• In model years 1987-1989, 1991, 1994-1995, and 1996, two brake bulb sizes are listed simultaneously, with the applicable fitment determined by the headlamp configuration present on the vehicle.
• The BAY15d bayonet base shared by the 1157 and 2057 is an offset-pin base, meaning the two pins are positioned at different heights to prevent incorrect installation orientation.
• The 198 wedge bulb, at 2W, operates at a substantially lower power level than either the 1157 or 2057, indicating it serves a functionally different role within the brake lighting circuit on the configurations where it is specified.