The Mack RB front and rear turn signal bulb size is 1157 for this truck model. The replacement chart covers vehicle production years from 1989 to 1997.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mack RB uses the 1157 bulb for both its front and rear turn signals across the 1989-1997 model years.
The 1157 is a dual-filament bulb, meaning it contains two separate filaments within a single housing, allowing it to serve more than one lighting function simultaneously.
It operates on a 12-volt electrical system and draws 21 watts on its high-intensity filament and 5 watts on its low-intensity filament.
The 1157 uses a BAY15d bayonet base, which features two offset pins at different heights to ensure correct orientation during installation and prevent incorrect fitment.
The 1157 conforms to ANSI standards and is recognized across both the United States and Canada, reflecting a standardized specification shared across North American automotive applications.
Because the front and rear turn signal positions on the Mack RB share the same bulb type, a single 1157 bulb serves as a direct replacement for either location throughout the full 1989-1997 production span.