GMC S370 front and rear side marker bulbs utilize a 63 size across both positions. The replacement chart covers 1951 through 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 S370 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 American National Standards Institute's classification system for lamps used in the United States and Canada.
The 63 bulb operates on a 12-volt electrical system, consistent with the standard automotive electrical architecture of the period.
At 0.63 watts, the 63 bulb draws very low current, reflecting its role as a marker lamp rather than a primary illumination source.
The 63 bulb is a single-filament type, meaning it serves one lighting function only, with no dual-mode capability such as combined running and brake light operation.
The BA9s base is a miniature bayonet fitting with a 9mm collar, a compact base type commonly found in indicator and marker lamp applications.
The front and rear side marker positions on the GMC S370 share the same bulb specification across all listed model years, indicating a uniform fitment requirement for both locations.