The GMC R1500 Suburban uses a 168 bulb size for front side marker applications and a 194 bulb size for rear side marker positions. The replacement chart covers 1987 to 1991 model 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 R1500 Suburban uses two distinct bulb sizes for its side marker positions across the 1987-1991 model years: size 168 for the front and size 194 for the rear.
Both the 168 and 194 bulbs conform to ANSI standards recognized in the United States and Canada, placing them within a regulated specification framework for miniature automotive lighting.
The 168 and 194 are both classified as miniature wedge bulbs with a T10 form factor, meaning they share the same physical base type despite being different part numbers.
Because both bulbs use a T10 wedge base, the distinction between them lies in wattage rather than base compatibility. The 168 operates at 4.9W while the 194 operates at 3.78W, both on a 12V system.
The lower wattage of the 194 rear side marker bulb means it produces less power draw than the 168 used at the front, a factor relevant to electrical load calculations.
Although the 168 and 194 share a T10 wedge base, substituting one for the other would result in an incorrect wattage for that position, as the specifications assign each bulb to a specific location.
The T10 wedge base design on both bulbs means installation requires no separate socket hardware; the bulb seats directly into a compatible wedge-type holder.
The 12V operating voltage on both bulbs aligns with the standard electrical system voltage found in conventional automotive applications of that era.