The GMC C1500 side marker utilizes a 194 bulb size for illumination across all listed vehicle applications. Data for 194 bulb size requirements covers the range from 1995 to 1999.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The two bulb types specified across the GMC C1500 side marker positions are the 194 and the 168, both of which are ANSI-standard miniature wedge bulbs sharing the T10 form factor and a 12-volt operating voltage.
Although the 194 and 168 share the same T10 wedge form factor, they are not electrically identical. The 194 operates at 3.78 watts, while the 168 operates at 4.9 watts, meaning the two types draw different amounts of current despite their physical similarity.
The front side marker position on the GMC C1500 used the 168 bulb from 1979-1986, then transitioned to the 194 bulb from 1988 onward through 1999.
The 194 bulb is the sole bulb type specified for the rear side marker position on the C1500, covering model years 1979-1980 and 1993-1999.
For the 1990-1991 front side marker, the 194 bulb specification carries a conditional note stating it applies to vehicles fitted with halogen capsule headlamps, indicating a trim or package dependency for those two model years.
The T10 wedge base is a tool-free, push-in socket design, which is a standard fitment method across both the 194 and 168 bulb types used in this application.
Because the 194 and 168 share the T10 wedge base, a 168 bulb is physically capable of seating in a socket designed for a 194, and vice versa. The wattage difference between the two types, however, means substitution could affect circuit load and lens brightness relative to the original specification.
Both the 194 and 168 are classified under ANSI standards recognized in the United States and Canada, placing them within a standardized designation system that defines their electrical and physical parameters.