GMC Astro front and rear turn signal bulbs both utilize a 1073 bulb size across all configurations. The replacement chart covers vehicle production spanning 1984 to 1988 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 1073 is an ANSI-standard single-filament bulb with a BA15s bayonet base, rated at 12 volts and 13 watts.
The BA15s designation refers to a single-contact bayonet base with a 15mm collar, a common format in automotive lighting applications.
The GMC Astro Tiltmaster uses the 1073 bulb for both front and rear turn signals across the 1984-1988 model years.
The 1073 is a lower-wattage variant of the 1156 bulb, which shares the same BA15s base but operates at a higher wattage of approximately 26.9 watts.
Because the 1073 and 1156 share the same BA15s base, they are physically interchangeable in the socket, though their wattage ratings differ and this can affect turn signal flash rates or load-sensitive circuits.
The single-filament construction of the 1073 means it serves a dedicated switching function, as opposed to dual-filament bulbs that handle multiple lighting roles from one housing.
The 1073 bulb specification applies uniformly to the Tiltmaster variant across all listed model years, with no differentiation between front and rear positions.