The GMC K2500 side marker requires a 194 bulb size for proper illumination of the exterior lighting housing. Available data for the specified component covers the range from 1995 through 2000.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 194 bulb is the most widely used size across the GMC K2500's side marker specifications, appearing in both front and rear positions across the majority of model years covered.
The 194 is a T10 miniature wedge bulb rated at 12V and 3.78W, conforming to ANSI standards for the US and Canadian markets.
The 168 bulb shares the same T10 miniature wedge form factor as the 194 but draws more power at 4.9W, making the two bulbs physically similar yet electrically distinct.
The GMC K2500 front side marker used the 168 bulb from 1979-1986, then transitioned to the 194 from 1988 onward through the 2000 model year.
Although the 194 and 168 share a T10 wedge base, their differing wattage ratings means one is not a direct drop-in substitute for the other without accounting for the electrical difference.
The 1990-1991 GMC K2500 front side marker specifies the 194 bulb specifically with the Halogen Capsule Headlamp configuration, indicating a conditional fitment tied to the headlamp type on those model years.
The rear side marker on the 1979 GMC K2500 uses the 67 bulb, a single-filament BA15s bayonet-base bulb rated at 12V and 8W, which is a different base type entirely from the wedge-style 194 used in all other rear side marker years listed.
The 67 bulb uses a BA15s bayonet base, which is physically incompatible with the T10 wedge socket used by both the 194 and 168 bulbs, making cross-substitution between the 67 and the other two types impossible without a socket adapter.
The rear side marker shifted from the 67 bayonet-base bulb in 1979 to the 194 wedge bulb by 1980, representing a socket-type change that affects hardware compatibility between those two model years.
All three bulb types listed across these specifications, the 194, 168, and 67, conform to ANSI standards applicable in both the United States and Canada.