GMC C35 Back Up Light Bulb Size

GMC C35 back up light bulb size specifications include 1156 and 199 bulb options for this vehicle model. The replacement chart covers 1973 to 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
1976-1978	1156
1975	199
1973-1974	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. Variant of 1156. 12V, 21W.	199

Other Locations

Additional Notes

The 1156 is the most frequently specified back up light bulb for the GMC C35, appearing across five of the six model years listed: 1973-1974 and 1976-1978.
The 1156 is an ANSI-standard single-filament bulb rated at 12 volts and 21 watts, fitted with a BA15s bayonet base.
The BA15s bayonet base uses a single contact pin, which determines the physical mounting and electrical connection method for the bulb in its socket.
The 1975 GMC C35 is the only model year in the listed specifications that calls for a 199 bulb rather than the 1156.
The 199 is classified as a variant of the 1156, sharing the same ANSI-standard single-filament construction, BA15s bayonet base, 12-volt rating, and 21-watt output.
Despite their shared electrical and physical characteristics, the 199 and 1156 are distinct part numbers, and the year-specific fitment data lists them separately rather than interchangeably.