Peterbilt 579 Side Marker Bulb Size

The Peterbilt 579 side marker utilizes a 3157 bulb size for the lighting components located on the exterior of the vehicle. Data for the specific bulb requirements covers the range from 2017 to 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
2017-2020	3157

Bulb Specifications

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

Other Locations

Additional Notes

The Peterbilt 579 uses the 3157 bulb for its side marker application across the 2017-2020 model years.
The 3157 is an ANSI-standardized bulb type, meaning its physical and electrical specifications are governed by a recognized North American standard shared across the United States and Canada.
The 3157 is a dual-filament bulb, which means it contains two separate filaments operating at different wattages within a single housing, rated at 27W for the high-intensity filament and 7W for the low-intensity filament.
The bulb operates on a 12-volt electrical system, consistent with standard automotive and commercial truck electrical architecture.
The T25 designation refers to the wedge-style base of the bulb, which seats directly into a socket without a separate metal base, relying on the glass envelope itself to make the electrical connection.
Because the 3157 is a dual-filament type, substituting it with a single-filament equivalent such as the 3156 would result in the loss of one lighting function at that socket position.