GMC W6500 Forward front side marker bulbs use 194 or 1157 size, while rear side marker bulbs use 194 size. The replacement chart covers vehicle production from 1987 to 1996 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 W6500 Forward uses the 194 bulb as the dominant type across both front and rear side marker positions throughout its model year range.
The 194 is a T10 miniature wedge bulb rated at 12V and 3.78W, operating under the ANSI standard applicable in both the United States and Canada.
The 1157 bulb appears in the front side marker position for the 1987 GMC W6500 Forward in the Medium Duty trim, making it the only position and year where this bulb type is specified.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W/5W output, which reflects its two-filament design serving separate brightness levels.
The BAY15d bayonet base of the 1157 is physically and electrically distinct from the wedge base of the 194, meaning the two bulb types are not interchangeable.
Front side marker entries for 1993-1996 carry the Tiltmaster designation, indicating those model years correspond to a specific cab-over configuration of the W6500 Forward.
Rear side marker entries for 1988-1992 carry the Medium Duty designation, while the 1987 and 1993-1995 rear side marker entries do not carry a trim designation, reflecting different fitment contexts within the same model line.
The 1987 front side marker position lists two separate entries, one for the 194 and one for the 1157 under the Medium Duty designation, indicating that bulb selection for that year depends on the specific trim or configuration of the vehicle.