Mack RW front and rear turn signal bulbs utilize a 1157 bulb size for this truck model. The replacement chart covers vehicle production spanning 1985 to 1993.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 1157 is the sole bulb type specified for the Mack RW across all listed model years and positions, covering both the front and rear turn signals from 1985-1993.
The 1157 is a dual-filament bulb, meaning it contains two separate filaments within a single envelope, allowing it to serve two distinct lighting functions at different wattages.
The 1157 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 prevent incorrect insertion and ensure proper filament orientation.
The 1157 conforms to ANSI standards and is recognized in both the United States and Canada, reflecting a standardized specification shared across North American markets.
Because the Mack RW uses the same 1157 bulb for both the front and rear turn signal positions across all listed years, the two positions are directly interchangeable with one another.
The BAY15d base of the 1157 is not universally interchangeable with single-filament bayonet bases such as the BA15s, as the dual-pin offset configuration is specific to dual-filament applications.