Peterbilt 579 Parking Light Bulb Size

The Peterbilt 579 parking light utilizes 3157 and 4157 bulb sizes for the exterior lighting system on the front of the truck. Available data for the specified components covers the period from 2013 through 2020.

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

Bulb Size by Year Range

Years	Bulb Size
2020	3157
2019	4157
2018	3157
2013-2017	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 parking light uses two bulb types across its model years: the 3157 and the 4157, both of which conform to ANSI standards recognized in the United States and Canada.
Both the 3157 and 4157 are dual-filament wedge bulbs built to the T25 form factor, operating at 12 volts with a 27W/7W power rating, where the higher wattage filament serves the brighter function and the lower wattage filament serves the dimmer function.
The dual-filament design allows a single bulb to handle two lighting functions simultaneously, which is a common arrangement in combined parking and stop light assemblies.
The Peterbilt 579 (2013-2017, 2019) uses the 4157 bulb for the parking light position, while the 2018 and 2020 model years use the 3157.
Despite sharing identical electrical specifications, the 3157 and 4157 are distinct part numbers and are not confirmed as interchangeable for the Peterbilt 579 parking light position.
The T25 designation refers to the bulb's wedge base size, which determines physical socket compatibility independent of the filament or voltage specifications.
The 27W/7W power rating is consistent across both bulb types, meaning neither the 3157 nor the 4157 draws more power than the other in this application.