GMC General front turn signal bulbs utilize 1073 or 1156 size specifications, while rear turn signal bulbs use 1073 or 1157 size configurations. The replacement chart covers 1984 through 1988 model 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 Tiltmaster uses three distinct bulb types across its front and rear turn signal positions: the 1073, 1156, and 1157, all of which conform to ANSI standards recognized in both the United States and Canada.
The 1073 is the most frequently specified bulb across both front and rear turn signal positions on the GMC Tiltmaster, appearing in seven of the ten total position-year combinations covered by these specifications.
The 1073 and 1156 are both single-filament bulbs sharing the same BA15s bayonet base, which means the socket type is physically identical between them. However, their wattage ratings differ, with the 1073 rated at 13W and the 1156 rated at 21W.
Because the 1073 and 1156 share the BA15s base, physical fitment in the socket is possible for either bulb, but substituting one for the other results in a different light output due to the wattage difference.
The 1157, specified for the 1986 Tiltmaster rear turn signal, is a dual-filament bulb rated at 21W and 5W on its respective filaments. It uses a BAY15d bayonet base, which is a different base type from the BA15s used by the 1073 and 1156.
The BAY15d base of the 1157 is not interchangeable with the BA15s base of the 1073 or 1156, as the pin offset on a BAY15d base is designed to prevent incorrect installation in single-filament sockets.
The front turn signal position on the Tiltmaster alternates between the 1073 and 1156 across the 1984-1988 model years, with no single bulb type used consistently throughout that span.
All three bulb types operate on a 12V electrical system, which is standard for automotive applications of this era.