GMC 3500 front turn signal bulbs utilize 1156, 1034, or 1073 size specifications, while rear turn signal bulbs use 1073 or 1034 sizes. The replacement chart covers 1960 through 1966 production years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC 3500 turn signal bulb specifications for the 1960-1966 model years reference three ANSI-standard bulb types: the 1156, 1034, and 1073, all rated at 12 volts.
The 1073 bulb is the most frequently specified type across both front and rear turn signal positions in the GMC 3500, appearing in the rear position for six of the seven model years covered.
The 1073 is a single-filament bulb with a BA15s bayonet base rated at 13W, making it a lower-wattage variant of the 1156.
The 1156 is also a single-filament bulb with a BA15s bayonet base, but it operates at 21W, drawing significantly more power than the 1073.
Because the 1156 and 1073 share the same BA15s bayonet base, physical fitment between the two is possible, but their wattage ratings differ and substitution may affect circuit behavior or lighting output.
The 1034 is a dual-filament bulb with a BAY15d bayonet base, which is physically distinct from the BA15s base used by both the 1156 and 1073, making cross-substitution between these types mechanically incompatible.
The 1034 is rated at 21/5W, with the dual-filament design allowing it to serve two separate functions, such as turn signaling and running light operation, within a single housing.
The 1034 is described as a variant of the 1157, a widely recognized dual-filament automotive bulb, indicating shared electrical and functional characteristics between the two types.
The GMC 3500 front turn signal used the 1034 in 1961-1962 and 1964-1965, while the 1960 and 1966 model years used the single-filament 1156, reflecting a non-uniform specification across the production run.
The rear turn signal position on the 1962 GMC 3500 is the only rear application in the covered years specified for the 1034 bulb, while all other rear positions across the same span call for the 1073.