GMC R2500 Back Up Light Bulb Size

The GMC R2500 back up light uses a 1156 bulb size for this vehicle model. The replacement chart covers 1987 to 1989 production years with corresponding bulb specifications.

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
1987-1989	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 1156 is the sole bulb type listed for the GMC R2500 back up light across the 1987-1989 model years.
The 1156 is an ANSI-standardized bulb recognized in both the United States and Canada, meaning it conforms to a defined set of electrical and physical standards shared across those markets.
It operates on a 12-volt circuit and draws 21 watts, which is typical of incandescent single-filament automotive bulbs used in back up light applications.
The 1156 uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin, distinguishing it from double-contact bayonet variants such as the BA15d.
Because the 1156 is a single-filament bulb, it serves one lighting function only, which aligns with its dedicated back up light role rather than a combined stop and tail application.
The BA15s base type is a widely produced standard, meaning the 1156 is broadly interchangeable with other bulbs sharing that base only when voltage, wattage, and application requirements also match.