GMC 100 front and rear turn signal bulbs utilize 3 distinct sizes including 1034, 1073, and 1129, with the front position accommodating all 3 sizes and the rear position using 1073 or 1129 bulb configurations. The replacement chart covers 1951 through 1959 model years with corresponding bulb size specifications for each production year.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC 100 turn signal bulb specifications cover the 1951-1959 model years, with three distinct bulb types appearing across the front and rear positions: the 1034, 1073, and 1129.
The 1129 bulb is the most frequently specified type in these listings, serving as both the front and rear turn signal bulb for the GMC 100 from 1951-1955.
The 1073 bulb is specified for both the front and rear turn signal positions from 1956-1959, with the exception of the 1959 front turn signal, which uses the 1034 instead.
The 1034 and 1129 are both dual-filament bulbs operating at 12V with a 21/5W output and sharing the BAY15d bayonet base, which means they are physically and electrically similar to one another.
Both the 1034 and 1129 are described as variants of the 1157, a widely recognized dual-filament automotive bulb, which places them within the same broad compatibility family.
The 1073 is a single-filament bulb with a BA15s bayonet base, rated at 12V and 13W, and is described as a lower wattage variant of the 1156. Its single-filament design and different base type make it physically incompatible with the dual-filament 1034 and 1129 bulbs.
The shift from the dual-filament 1129 to the single-filament 1073 between the 1955 and 1956 GMC 100 represents a change in both filament count and base type, meaning the two bulbs are not interchangeable.
The 1959 front turn signal position is the only instance in these specifications where the 1034 is used, while the rear position for the same year retains the 1073, resulting in mismatched bulb types between front and rear for that model year.
All three bulb types conform to ANSI standards applicable in both the United States and Canada, indicating standardized electrical and physical tolerances across the listed part numbers.
The BAY15d base found on both the 1034 and 1129 features offset pins, a design that prevents incorrect insertion by ensuring the bulb can only be seated in one orientation within the socket.