GMC B6000 Back Up Light Bulb Size

The GMC B6000 back up light utilizes a single 1156 bulb size for the specified lighting component. Provided information covers a continuous span from 1980 through 1991 for the identified 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
1981-1991	1156 (Medium Duty)
1980	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 B6000 back up light uses the 1156 bulb across all model years represented in the specifications, from 1980 through 1991.
The 1156 is an ANSI-standard bulb recognized in both the United States and Canada, making it a widely available replacement type.
It is a single-filament bulb, meaning it serves one lighting function rather than combining two functions such as stop and tail into a shared housing.
The 1156 uses a BA15s bayonet base, a single-contact bayonet mount that locks into the socket with a twist rather than a threaded connection.
The bulb operates at 12 volts and draws 21 watts, which is consistent with standard automotive incandescent back up light applications.
Model years 1981 through 1991 carry a Medium Duty designation alongside the 1156 specification, indicating a vehicle classification rather than a variation in the bulb itself.
The 1980 model year shares the same 1156 bulb size but does not carry the Medium Duty designation in the specifications.
Because the BA15s base is a single-contact design, it is not interchangeable with the BA15d double-contact bayonet base used on dual-filament bulbs such as the 1157, despite the similar physical appearance of the two base types.