Peterbilt 579 Turn Signal Bulb Size

Peterbilt 579 front turn signal bulbs use 3157 and 4157 sizes for replacement. The chart covers 2013 to 2020 production years with corresponding bulb size specifications.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Front Turn Signal

Years	Bulb Size
2017-2020	3157
2013-2016	4157

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3157
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	4157

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Additional Notes

The Peterbilt 579 front turn signal uses two distinct bulb types across its model years: the 3157 for 2017-2020 and the 4157 for 2013-2016.
Both the 3157 and 4157 are ANSI-standardized bulbs recognized in the United States and Canada, meaning they conform to a shared set of electrical and physical standards within those markets.
Each bulb is a dual-filament type, which allows a single housing to serve two lighting functions, typically combining turn signal and parking light operation within one unit.
Both bulbs operate on a 12-volt system with a wattage rating of 27W on the high filament and 7W on the low filament, making their power draw identical across all listed model years.
The 3157 and 4157 share the same T25 wedge base form factor and identical voltage and wattage ratings, yet they carry different ANSI designations, which reflects a difference in their contact configuration rather than their general size or power characteristics.
Because the 3157 and 4157 differ in contact configuration, substituting one for the other in the Peterbilt 579 front turn signal socket is not straightforward, and fitment depends on the specific socket design present in a given model year.