The GMC Brigadier front and rear turn signal bulbs utilize 1073 and 1157 bulb sizes for replacement applications. The replacement chart covers vehicle production spanning 1984 to 1988 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 two bulb types specified across all GMC Brigadier (Tiltmaster) turn signal positions are the 1073 and 1157, both of which are ANSI-standardized bulbs recognized in the United States and Canada.
The 1073 is a single-filament bulb rated at 12V and 13W, fitted with a BA15s bayonet base. It functions in a single-intensity capacity, meaning it serves one lighting purpose per position rather than switching between two brightness levels.
The 1157 is a dual-filament bulb rated at 12V with a 21W/5W output, fitted with a BAY15d bayonet base. The two filaments allow it to operate at different wattages, typically corresponding to a brighter active signal and a dimmer running light state.
The BA15s base of the 1073 and the BAY15d base of the 1157 are not interchangeable. The BAY15d base has offset locating pins to prevent incorrect installation, while the BA15s base has symmetrical pins, making the two physically incompatible despite their similar appearance.
For the front turn signal position, the GMC Brigadier (Tiltmaster) uses the 1073 in 1984 and 1988, while the 1157 is specified for 1985-1987.
For the rear turn signal position, the 1073 is specified for 1984-1987, while the 1988 model year uses the 1157.
The front and rear turn signal positions do not share the same bulb type within any single model year. In each year covered, one position uses the 1073 while the other uses the 1157.
The 1073 is described as a lower wattage variant of the 1156. Although the 1073 and 1156 share the same BA15s bayonet base, their wattage ratings differ, and the two are not specified as interchangeable within these fitments.