The Mack R front and rear turn signal bulb size is 1157 for this truck model. The replacement chart contains vehicle production years and bulb size specifications spanning 1981 to 1991.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mack R uses the 1157 bulb for both its front and rear turn signals across the 1981-1991 model years.
The 1157 is the sole bulb type specified across all turn signal positions in these specifications, making it the defining bulb for this application.
The 1157 is an ANSI-standardized bulb recognized in both the United States and Canada, meaning it conforms to a shared North American specification rather than a proprietary or regional standard.
As a dual-filament bulb, the 1157 contains two separate filaments within a single envelope, allowing it to serve two distinct lighting functions from one unit.
The 1157 operates on a 12-volt electrical system, which is standard for most commercial vehicles of this era.
Its two filaments are rated at 21 watts and 5 watts respectively, with the higher-wattage filament typically serving the active turn signal function and the lower-wattage filament serving a parking or running light function.
The 1157 uses a BAY15d bayonet base, a two-pin offset base design that physically prevents incorrect insertion by positioning the two pins at different heights along the base.
Because the front and rear turn signal positions share the same 1157 specification, a single bulb type covers all four turn signal sockets on the vehicle.