The GMC R2500 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 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 R2500 Suburban uses two distinct bulb sizes for its side marker lights across the 1987-1991 model years: the 168 for the front position and the 194 for the rear position.
Both the 168 and 194 are ANSI-standardized bulbs recognized across the United States and Canada, meaning they conform to a shared North American specification for miniature automotive lighting.
Both bulbs share the T10 miniature wedge form factor, a small, baseless design that seats directly into a wedge-style socket without requiring a separate metal base or bayonet fitting.
Both bulbs operate on a 12-volt circuit, consistent with the standard electrical architecture of passenger and light-duty vehicles of that era.
Although the 168 and 194 share the same T10 wedge form factor and voltage rating, they are not electrically identical. The 168 draws 4.9 watts while the 194 draws 3.78 watts, reflecting a difference in filament resistance and light output.
The wattage difference between the two bulbs means that substituting one for the other, despite their physical similarity, would alter the current draw and luminous output at whichever socket receives the incorrect bulb.