Peterbilt 320 Back Up Light Bulb Size

The Peterbilt 320 back up light utilizes 1156 and P21W bulb sizes for the rear illumination system on the vehicle. Available information spans the range of 1987 through 2017 for the specific components listed in the data.

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
2011-2017	1156
1996-2009	1156
1995	1156
1995	1156 (With Halogen Capsule Headlamps)
1994	1156
1994	1156 (With 4 Round Headlamps)
1993	1156
1993	1156 (With Halogen Capsule Headlamps)
1992	1156
1992	1156 (With 4 Rectangular Headlamps)
1991	1156
1990	1156
1990	1156 (With 4 Round Headlamps)
1988-1989	1156
1988-1989	1156 (With 4 Rectangular Headlamps)
1987	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 320 uses the 1156 bulb for its back up light across all specified model years from 1987 to 2017.
The 1156 is an ANSI-standard bulb recognized in both the United States and Canada, making it a widely available replacement type in North American markets.
The 1156 is a single-filament bulb, meaning it serves one lighting function only, which is consistent with its application in a dedicated back up light position.
The 1156 uses a BA15s bayonet base, a single-contact bayonet mount where the "s" denotes a single pin offset to one side, ensuring the bulb seats in one orientation only.
The 1156 operates at 12 volts and draws 21 watts, placing it in the standard low-voltage range typical of automotive electrical systems.
For the 1993 and 1995 Peterbilt 320, separate fitment entries exist for configurations with halogen capsule headlamps, though the back up light bulb size remains 1156 in both cases.
For the 1990 and 1994 Peterbilt 320, separate fitment entries exist for configurations with 4 round headlamps, with the back up light bulb size again specified as 1156.
For the 1988, 1989, and 1992 Peterbilt 320, separate fitment entries exist for configurations with 4 rectangular headlamps, and the back up light bulb size remains 1156 across those variants as well.
The BA15s bayonet base of the 1156 is not interchangeable with the BA15d base used on dual-filament bulbs such as the 1157, as the pin configurations differ between the two types.
The consistency of the 1156 specification across all listed headlamp configuration variants indicates that headlamp type on the Peterbilt 320 does not affect back up light bulb fitment.