GMC P60 Back Up Light Bulb Size

The GMC P60 back up light requires a single 1156 bulb size for the specified lighting component. Available information covers the period from 1983 through 1990 for the listed vehicle.

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
1983-1990	1156 (Medium Duty)

Bulb Specifications

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

Other Locations

Additional Notes

The GMC P60 (Medium Duty) uses the 1156 bulb for the back up light across all listed model years, spanning 1983-1990.
The 1156 is an ANSI-standardized bulb recognized across the United States and Canada, meaning it conforms to a defined set of electrical and physical standards shared between the two markets.
The 1156 operates on a 12-volt electrical system and draws 21 watts, which is typical for incandescent automotive signal and reverse lighting applications.
The 1156 is a single-filament bulb, distinguishing it from dual-filament variants such as the 1157, which serve functions requiring two brightness levels like combined stop and tail lighting.
The base type on the 1156 is a BA15s bayonet mount, where "BA15" refers to the 15mm pin spacing and "s" denotes a single-contact configuration. This base type is not interchangeable with double-contact bayonet bases such as the BA15d used on dual-filament bulbs.