GMC 100 front and rear side marker bulbs utilize a 63 size across both positions. The replacement chart covers 1951 to 1955 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 100 uses the 63 bulb for both front and rear side marker positions across the 1951-1955 model years.
The 63 bulb follows the ANSI standard, which is the recognized classification system for automotive and miniature lamps in the United States and Canada.
This bulb operates on a 12-volt electrical system, consistent with the standard automotive voltage adopted broadly during this era.
At 0.63 watts, the 63 bulb draws a very low amount of power, reflecting its role as a marker lamp rather than a primary illumination source.
The 63 bulb uses a BA9s base, which is a miniature bayonet-style single-contact base with a 9mm collar width, commonly found in low-wattage indicator and marker applications.
The single-filament construction of the 63 bulb means it serves only one lighting function, with no secondary circuit for braking or turn signals within the same housing.
The uniform use of the 63 bulb across all listed model years and both marker positions means a single bulb type covers the full side marker requirement for the GMC 100 from 1951 through 1955.