Peterbilt 567 Turn Signal Bulb Size

Additional Notes

• The front turn signal positions across the Peterbilt 567 lineup use three closely related bulb types: 3157, 4157, and 4157NA. All three share the same T25 wedge form factor, dual-filament design, 12V operating voltage, and 27W/7W wattage rating.
• The 4157NA is a natural amber glass variant of the 4157. The amber tint is built into the glass envelope itself rather than applied through a lens or coating, which affects color output at the source.
• The 4157NA was the specified front turn signal bulb for the Peterbilt 567 from 2014-2017.
• The 4157 (clear glass) replaced the 4157NA for the 2018 model year front turn signal position.
• The 3157 became the specified front turn signal bulb for the 2019-2020 model years.
• Although the 3157 and 4157 share identical electrical ratings and the same T25 wedge base, they carry different ANSI part numbers, which indicates a distinction in physical or performance characteristics that makes them non-interchangeable across all applications without verification.
• The dual-filament construction found in all three bulb types serves two circuits within a single housing, typically supporting both a running light function and a higher-intensity turn or brake signal function through the 7W and 27W filaments respectively.
• All three bulb types conform to ANSI standards applicable in both the United States and Canada, placing them within a regulated specification framework for automotive lighting.