GMC G15 Back Up Light Bulb Size

The GMC G15 back up light bulb size chart specifies 2 bulb options: 199 and 1156 sizes for this vehicle model. The replacement chart covers 1973 through 1978 production years with corresponding bulb size data.

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
1977-1978	199
1973-1976	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 21W.	199
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The GMC G15 back up light specifications cover model years 1973-1978, split across two bulb sizes: the 1156 for 1973-1976 and the 199 for 1977-1978.
Both the 1156 and 199 are ANSI-standardized bulbs recognized in the United States and Canada, each operating at 12 volts and 21 watts with a single filament.
The BA15s bayonet base is shared by both bulb types. This base style uses a single locating pin on the base collar, which locks the bulb into the socket with a push-and-twist motion.
The 199 bulb, used in the 1977-1978 GMC G15, is a variant of the 1156. Both share identical electrical ratings and the same BA15s base construction.
Because the 199 is a variant of the 1156 and both share the same base type and electrical ratings, physical and electrical compatibility between the two is closely related, though fitment should be confirmed against the specific socket design for the model year in question.