GMC C25 Suburban Back Up Light Bulb Size

The GMC C25 Suburban back up light uses 1156 and 199 bulb sizes for replacement applications. 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
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 dominant back up light bulb across the GMC C25 Suburban's listed model years, appearing in 1973-1974 and 1976-1978.
The 1156 is an ANSI-standardized single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
A single-filament design means the 1156 serves one lighting function only, distinguishing it from dual-filament bulbs that handle two functions such as braking and running light duties simultaneously.
The BA15s bayonet base uses a single locating pin, which locks the bulb into its socket at a fixed rotational position.
The 1975 GMC C25 Suburban uses the 199 bulb rather than the 1156 for its back up light.
The 199 shares the same ANSI classification, BA15s bayonet base, 12V rating, and 21W output as the 1156, and is formally designated a variant of it.
Despite their technical similarities, the 1156 and 199 carry distinct ANSI part numbers, and substitution between them warrants verification of socket fitment before use.