GMC G35 Back Up Light Bulb Size

The GMC G35 back up light uses a 199 or 1156 bulb size for replacement purposes. The replacement chart covers vehicle production spanning 1973 to 1978.

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
1974-1976	1156
1973	199

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

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Additional Notes

The GMC G35 back up light specifications reference two bulb types across the 1973-1978 model years: the 199 and the 1156.
Both the 199 and 1156 are ANSI-standardized bulbs recognized in the US and Canada, each operating at 12 volts with a 21-watt output and a single filament.
The shared BA15s bayonet base between the 199 and 1156 means both bulbs use the same single-contact base configuration, where a single pin aligns the bulb within the socket.
The 199 is classified as a variant of the 1156, which accounts for their identical voltage, wattage, filament count, and base type.
The GMC G35 used the 1156 bulb for the 1974-1976 model years in the back up light position.
The 199 bulb was specified for the 1973, 1977, and 1978 model years of the G35 back up light.
Despite the physical and electrical similarities between the 199 and 1156, the variant relationship between them warrants attention when sourcing replacements, as manufacturer fitment data distinguishes between the two across different model years.