The GMC M300 front and rear turn signal bulb sizes include 1073, 1034, and 1129 specifications. The replacement chart covers vehicle production years spanning 1954 to 1957.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC M300 turn signal specifications cover model years 1954 through 1957 and reference three distinct ANSI-standard bulb types: 1073, 1034, and 1129.
The 1129 bulb is a dual-filament type rated at 12V with a 21/5W output, mounted on a BAY15d bayonet base. It is classified as a variant of the 1157 and serves both the front and rear turn signals on the GMC M300 for the 1954-1955 model years.
The BAY15d base used by the 1129 features offset pins, which physically prevents it from being seated in a single-filament BA15s socket. This makes the 1129 non-interchangeable with the 1073 at the socket level.
The 1073 bulb is a single-filament type rated at 12V and 13W, using a BA15s bayonet base. It is described as a lower wattage variant of the 1156 and is specified for the front turn signal position on the 1957 M300.
The 1034 bulb shares the same BAY15d base and 12V/21/5W dual-filament configuration as the 1129, and is also a variant of the 1157. Despite these similarities, the 1034 and 1129 are distinct part numbers and are not listed as interchangeable within these specifications.
On the 1956 GMC M300, the front and rear turn signal positions use different bulb types: the front takes the 1034 while the rear takes the 1073. This reverses the positional assignment seen in the 1957 model year, where the 1073 moves to the front and the 1034 moves to the rear.
All three bulb types listed in the specifications conform to ANSI standards recognized in both the United States and Canada, indicating a standardized electrical and physical specification rather than a proprietary fitment.