GMC FC100 front and rear side marker bulbs utilize a 63 size across both positions. The replacement chart covers 1950 to 1952 production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC FC100 uses the 63 bulb for both front and rear side marker positions across the 1950-1952 model years.
The 63 is an ANSI-standardized bulb recognized across the United States and Canada, indicating a regionally consistent specification.
The 63 bulb operates on a 12-volt electrical system, which aligns with the standard automotive electrical architecture of the period.
At 0.63 watts, the 63 bulb draws minimal current, a characteristic typical of small indicator and marker lamps rather than primary lighting sources.
The 63 bulb uses a BA9s base, a miniature bayonet fitting with a 9mm cap width and a single pin, distinguishing it from the more common BA15s base found in larger automotive bulbs.
The single-filament construction of the 63 bulb means it serves one lighting function only, with no dual-intensity capability such as that found in stop/tail combination bulbs.
The identical bulb specification across both the front and rear side marker positions on the GMC FC100 means a single bulb type services all four side marker sockets on the vehicle.