GMC R2500 Suburban Back Up Light Bulb Size

The GMC R2500 Suburban back up light utilizes 1156 and P21W bulb sizes according to the provided data. Information for the specified components covers the period from 1987 through 1991.

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
1987-1991	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 GMC R2500 Suburban uses the 1156 bulb for the back up light across all listed model years, spanning 1987-1991.
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 across manufacturers.
It is a single-filament bulb, which means it serves one lighting function only, as opposed to dual-filament bulbs that handle two functions such as braking and running light from a single unit.
The 1156 operates at 12 volts and 21 watts, consistent with standard 12V automotive electrical systems.
The bulb uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width. The single-contact design aligns with the bulb's single-filament construction.
Because the BA15s base is a single-contact type, it is not interchangeable with BA15d bases, which carry two contacts and are found on dual-filament bulbs. Substituting one for the other is not physically compatible.