GMC 1500 Series front turn signal bulbs use 1156 or 1073 size, while rear turn signal bulbs use 1034 or 1073 size. The replacement chart covers 1960 through 1965 vehicle 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 1500 Series front turn signal uses two distinct bulb types across the 1960-1965 model years: the 1156 and the 1073.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and classified under the ANSI standard applicable in the US and Canada.
The 1073 shares the same BA15s bayonet base and 12V operating voltage as the 1156 but draws only 13W, making it a lower-wattage variant of that bulb type.
Because the 1156 and 1073 share the same BA15s base, physical fitment between the two is possible, but their wattage difference means one is not a direct electrical equivalent of the other.
The 1034 is a dual-filament bulb rated at 12V with a 21/5W output, fitted with a BAY15d bayonet base, and is classified as a variant of the 1157 under the ANSI standard.
The BAY15d base of the 1034 is mechanically distinct from the BA15s base used by the 1156 and 1073, meaning these bulb types are not interchangeable with one another.
The GMC 1500 Series rear turn signal uses the 1034 in 1961, 1963, and 1965, while the 1073 is specified for 1960, 1962, and 1964, reflecting an alternating fitment pattern across those years.
The dual-filament design of the 1034 allows it to serve two independent lighting functions within a single housing, which is a characteristic relevant to combined stop and turn signal assemblies.
The front turn signal for the GMC 1500 Series uses the 1073 in 1960 and 1963, while the 1156 is specified for 1961-1962 and 1964-1965.
All three bulb types in these specifications, the 1156, 1073, and 1034, operate on a 12V electrical system, consistent with the standard automotive voltage of that era.