GMC C7000 Back Up Light Bulb Size

The GMC C7000 back up light utilizes 1156 and 1073 bulb sizes for illumination purposes. Available information covers the specific range of years from 1979 through 1990.

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
1984-1990	1156 (Medium Duty)
1984-1990	1073 (Tiltmaster)
1981-1983	1156 (Medium Duty)
1979-1980	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Lower wattage variant of 1156. 12V, 13W.	1073

Other Locations

Additional Notes

The GMC C7000 back up light specifications cover model years 1979-1990 and reference two bulb types: the 1156 and the 1073.
Both the 1156 and 1073 are ANSI-standard single-filament bulbs sharing the same BA15s bayonet base, operating at 12 volts.
The primary distinction between the two bulbs is wattage. The 1156 is rated at 21W, while the 1073 is rated at 13W, making the 1073 a lower-output variant of the 1156.
Although both bulbs share the BA15s bayonet base, the wattage difference means they are not interchangeable without affecting light output performance.
The GMC C7000 Tiltmaster configuration uses the 1073 bulb for the back up light across model years 1984-1990.
The Medium Duty configuration of the C7000 uses the 1156 bulb across model years 1983-1990.
For model years 1979-1982, the specifications list only the 1156 bulb with no sub-model designation noted.
The BA15s bayonet base is a single-contact base, consistent with the single-filament design of both the 1156 and 1073 bulbs.