The GMC FC150 front and rear turn signal bulbs both utilize a 1129 size bulb for optimal illumination. The replacement chart covers 1950 through 1952 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 1129 bulb is the sole turn signal bulb type listed for the GMC FC150 across all documented model years, appearing in both front and rear turn signal positions for 1950-1952.
The 1129 is an ANSI-standardized bulb recognized in both the United States and Canada, operating at 12 volts with a dual-filament design rated at 21/5 watts.
The dual-filament construction of the 1129 allows it to serve two distinct lighting functions within a single housing, with the higher-wattage filament handling the active turn signal and the lower-wattage filament handling a secondary function such as a running or parking light.
The 1129 uses a BAY15d bayonet base, a two-pin offset base type that physically prevents incorrect insertion by positioning its two pins at different heights along the base.
The 1129 is documented as a variant of the 1157 bulb. These two types share the BAY15d base and dual-filament configuration, though they differ in electrical characteristics, meaning they are not directly interchangeable without verifying voltage and wattage compatibility with the vehicle's circuit.