The Mack MR front and rear turn signal bulb size is 1157 for this truck model. The replacement chart covers vehicle production years from 1981 to 1997 with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mack MR uses the 1157 bulb for both its front and rear turn signals across all model years from 1981-1997.
The 1157 is a dual-filament bulb, meaning it contains two separate filaments within a single glass envelope, each rated for a different wattage.
The two filaments in the 1157 are rated at 21W and 5W, where the higher-wattage filament typically serves the turn signal or brake function and the lower-wattage filament serves a secondary function such as a running light.
The 1157 operates on a 12-volt electrical system, which is standard for automotive and commercial truck applications.
The 1157 uses a BAY15d bayonet base, a two-pin offset base design that prevents incorrect installation by ensuring the bulb can only be seated in one orientation, aligning each filament with its intended circuit.
The 1157 conforms to ANSI standards and is recognized in both the United States and Canada, reflecting its widespread use across North American vehicle applications.
Because the front and rear turn signal positions on the Mack MR share the same 1157 specification, a single bulb type serves both locations across the entire 1981-1997 production span.
The BAY15d base of the 1157 is not interchangeable with single-filament bayonet bases such as the BA15s, and substituting a single-filament bulb in a dual-filament socket would result in loss of one lighting function.