GMC C7000 front and rear side marker bulbs utilize 194, 1157, and 1895 bulb sizes depending on location and model variation. The replacement chart covers 1979 through 1990 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC C7000 front side marker positions across 1979-1990 draw from two distinct bulb types: the 194 and the 1157, with fitment determined by model year and trim configuration rather than a single universal specification.
The 194 is a T10 miniature wedge bulb rated at 12V and 3.78W under the ANSI standard. Its wedge base design means it requires no separate socket retainer, as the base itself locks into the housing.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W high filament and a 5W low filament. Its dual-filament construction and bayonet base make it physically and electrically incompatible with sockets designed for the single-filament 194.
On the GMC C7000, the 1157 appears in the front side marker position for Medium Duty configurations in 1979, 1980, 1981, 1983, 1985, and 1987, while the 194 serves the same position in those same years when the vehicle is equipped with 2 rectangular headlights.
The headlight configuration on the C7000 directly influences front side marker bulb fitment in 1979-1981, 1983, 1985, and 1987, where Medium Duty vehicles with 2 rectangular headlights use the 194 rather than the 1157.
From 1986 onward through 1990, the front side marker standardizes on the 194 across all listed configurations, with the 1157 no longer appearing in those model years except in 1987 Medium Duty variants without the rectangular headlight qualifier.
The rear side marker on the C7000 introduces a third bulb type, the 1895, which is a T5 miniature wedge bulb rated at 12V and 0.9W. At 0.9W, it operates at a significantly lower wattage than the 194 and is not interchangeable with it despite both using a wedge base format.
The 1895 rear side marker fitment is specific to Heavy Duty configurations in 1979 and 1980, while Medium Duty configurations in those same years use the 194 in the rear position.
From 1981 through 1990, the rear side marker on Medium Duty C7000 models uses the 194 exclusively, with the exception of 1985 and 1987, which revert to the 1157 in that position.
Because the 194 and 1157 share neither base type nor filament count, and the 194 and 1895 differ in wattage and physical size despite both being wedge-style bulbs, substitution between any of these three types without confirming the housing specification would result in an incorrect fit.