The Mack DMC front and rear turn signal bulb size specifications indicate a 1157 bulb for both applications. A replacement chart covering 1981 to 1986 model years documents the turn signal bulb sizes for this vehicle.
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 both the front and rear turn signals of the Mack DMC across all listed model years.
The 1157 is an ANSI-standardized bulb recognized in both the United States and Canada, meaning it conforms to a defined set of electrical and physical standards shared across those markets.
The 1157 is a dual-filament bulb, which means it contains two separate filaments within a single envelope, allowing it to serve two distinct lighting functions from one unit.
The bulb operates on a 12-volt electrical system and carries a wattage rating of 21W on its high-intensity filament and 5W on its low-intensity filament, reflecting its dual-function design.
The 1157 uses a BAY15d bayonet base, a two-pin offset base type where the two pins are positioned at different heights to prevent incorrect installation orientation.
The BAY15d base is a keyed fitment, meaning a bulb with a standard BAY15d base where both pins sit at equal heights is not a direct mechanical substitute for the 1157.
The front and rear turn signal positions on the Mack DMC share the same 1157 bulb specification across all listed model years, indicating no positional difference in bulb requirements between those two locations.
The listed model years for the Mack DMC span 1981-1986, with the specifications covering 1981-1982 and 1984-1986.