Peterbilt 320 Tail Light Bulb Size

Additional Notes

• The Peterbilt 320 tail light specifications cover model years 1987 through 2017, with two distinct bulb types accounting for the majority of fitments across that span: the 1157 and the 2057.
• Both the 1157 and 2057 are ANSI-standard dual-filament bulbs sharing the BAY15d bayonet base, which means they are physically interchangeable in terms of socket fit, though their wattage ratings differ.
• The 2057 operates at 26.9W on its high-intensity filament and 8W on its low-intensity filament, compared to the 1157 at 21W and 5W respectively, making the 2057 the higher-output of the two types used in this application.
• The Peterbilt 320 (2011-2017) uses the 1157 exclusively for the tail light position, representing a shift from the 2057 that was specified for most prior model years.
• The 2057 is the specified tail light bulb for the Peterbilt 320 across model years 1987-2009, with certain years also listing an alternative fitment depending on headlamp configuration.
• The 198 is a miniature wedge bulb of the T5 form factor, rated at 12V and 2W, and is a single-filament low-wattage type, which stands in contrast to the dual-filament 1157 and 2057 used in the same tail light position on other configurations.
• For the 1993, 1995, 1996, and 1997 model years, the Peterbilt 320 tail light fitment depends on headlamp configuration, with certain headlamp types corresponding to the 198 bulb and others to the 2057.
• The 198 bulb appears only in years where a specific headlamp configuration is noted, such as 4 Round Headlamps, 4 Rectangular Headlamps, or Halogen Capsule Headlamps, indicating that the tail light bulb selection on those vehicles was tied to the overall lighting system variant installed.
• Because the 1157 and 2057 share the BAY15d bayonet base, a socket designed for one will physically accept the other, though the difference in filament wattage means the two types are not electrically identical and substitution may affect circuit behavior.
• The 198 wedge bulb uses a T5 base that is not compatible with the BAY15d bayonet socket used by the 1157 and 2057, so the 198 fitment represents a physically distinct socket type within the 320's tail light configurations.