GMC 3000 front turn signal bulbs utilized 1034 and 1073 sizes, while rear turn signal bulbs used 1073 and 1156 sizes. The replacement chart covers 1960 through 1966 model 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 3000 turn signal specifications reference three bulb types across both front and rear positions: the 1034, 1073, and 1156. All three conform to ANSI standards recognized in both the United States and Canada.
The 1034 and 1073 are the most frequently specified bulbs across the GMC 3000 turn signal positions, appearing in multiple model years for both front and rear applications.
The 1034 is a dual-filament bulb rated at 12V and 21/5W, fitted with a BAY15d bayonet base. Its dual-filament design means it serves two brightness levels within a single housing, a characteristic that distinguishes it from the single-filament types also listed.
The 1034 is described as a variant of the 1157. While the two share a BAY15d base, they are not identical, and substitution between them warrants attention to wattage and filament compatibility for the specific application.
The 1073 and 1156 both use a BA15s single-contact bayonet base, making their base type physically similar. However, the 1073 is rated at 13W while the 1156 is rated at 21W, classifying the 1073 as a lower-wattage variant of the 1156.
Because the 1073 and 1156 share the same BA15s base, physical fitment alone does not confirm interchangeability. The wattage difference between 13W and 21W can affect turn signal flash rates and circuit load expectations.
The GMC 3000 front turn signal uses the 1034 for 1961 and 1964-1966, while the 1073 is specified for 1960, 1962, and 1963. These two bulbs have different base types, BAY15d versus BA15s, meaning they are not interchangeable.
The rear turn signal on the GMC 3000 uses the 1156 for 1961-1964, the 1073 for 1960 and 1965-1966. Both share the BA15s base, but the wattage difference between the two positions across those years reflects a deliberate specification change rather than a simple substitution.
The 1034 is specified exclusively for the front turn signal position on the GMC 3000 and does not appear in any rear turn signal application within these specifications. Its dual-filament design is distinct from the single-filament bulbs used at the rear.
All three bulb types operate at 12V, consistent with the standard automotive electrical system voltage of the era covered by these specifications.