The GMC F350 front and rear turn signal bulbs utilize 1073 and 1129 sizes. The replacement chart covers 1953 through 1957 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 GMC F350 turn signal specifications cover model years 1953 through 1957, with two distinct bulb types used across that span depending on the year.
The 1129 bulb is a dual-filament type rated at 12V and 21/5W, using a BAY15d bayonet base. The dual-filament design allows a single bulb to serve two brightness levels, which is typical in combined stop and turn signal applications.
The 1073 bulb is a single-filament type rated at 12V and 13W, using a BA15s bayonet base. It is a lower wattage variant of the more common 1156 bulb.
Both bulb types conform to ANSI standards recognized in the United States and Canada.
The GMC F350 (1953-1955) uses the 1129 bulb for both front and rear turn signals.
The 1956-1957 model years transitioned to the 1073 bulb for both front and rear turn signal positions.
The BA15s base of the 1073 and the BAY15d base of the 1129 are not interchangeable. The BAY15d base has offset pins to prevent incorrect installation of a single-filament bulb in a dual-filament socket, making cross-substitution between these two types physically incompatible.
Because the 1073 is a single-filament bulb and the 1129 is a dual-filament bulb, they serve different circuit configurations and cannot be used as functional substitutes for one another regardless of base compatibility.