GMC C3500 front and rear side marker bulbs utilize 194, 168, and 67 bulb sizes across different positions on the vehicle. The replacement chart covers 1979 to 2000 model 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 194 bulb is the most widely used type across the GMC C3500 side marker specifications, appearing in both front and rear positions across the majority of model years covered.
The 194 is an ANSI-standard miniature wedge bulb in the T10 form factor, rated at 12V and 3.78W, and is recognized in both the US and Canada.
The 168 bulb shares the same T10 miniature wedge form factor as the 194 but draws more power at 4.9W versus 3.78W, making the two electrically distinct despite their physical similarities.
The GMC C3500 front side marker used the 168 bulb from 1979-1986, then transitioned to the 194 from 1988 onward through 2000.
Because the 168 and 194 share the T10 wedge base, they are physically interchangeable in the socket, but their wattage difference means one is not a direct electrical equivalent of the other.
The 1990-1991 front side marker 194 fitment carries a conditional note specifying it applies to vehicles with Halogen Capsule Headlamps, indicating a trim or package dependency for those model years.
The 67 bulb, used in the 1979 GMC C3500 rear side marker, differs fundamentally from the 194 and 168 in that it uses a BA15s single-contact bayonet base rather than a wedge base, making it physically incompatible with sockets designed for T10 wedge bulbs.
The 67 bulb is rated at 8W, making it the highest-wattage bulb among the three types listed in these specifications, and it is described as a lower-wattage variant of the 1156 bulb family.
The rear side marker shifted from the 67 bayonet-base bulb in 1979 to the 194 wedge-base bulb by 1980, representing a change in both socket type and wattage for that position.
All three bulb types in these specifications, the 194, 168, and 67, are ANSI-standard bulbs recognized across the US and Canadian markets.