Peterbilt 325 Back Up Light Bulb Size

The Peterbilt 325 back up light utilizes 1156 and P21W bulb sizes for the rear illumination system. Data for the specified components covers the period from 2008 through 2015.

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
2011-2015	1156
2008-2009	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The Peterbilt 325 uses the 1156 bulb across all specified model years for the back up light position.
The years covered by these specifications are 2008-2009 and 2011-2015.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical characteristics are defined by a common North American standard shared across the United States and Canada.
The 1156 operates at 12 volts and draws 21 watts, which is consistent with standard automotive incandescent back up light applications.
The 1156 is a single-filament bulb, meaning it serves only one lighting function per socket, as opposed to dual-filament types that can handle two functions such as stop and tail from a single unit.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a bayonet cap with a 15mm base width and a single contact pin, which determines physical fitment into the socket.
The BA15s base is not interchangeable with the BA15d base, which carries two offset contact pins rather than one, so substitution between these base types is not possible even when the outer housing appears similar.
The 1156 should not be confused with the 1157, which shares a similar appearance but uses a BA15d dual-contact base and a dual-filament design, making the two types electrically and physically incompatible in most sockets.