The Mack DM 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 DM 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, allowing it to serve two distinct lighting functions at different wattages.
The bulb 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 is an offset dual-contact base. The offset pin placement prevents incorrect insertion, as the two pins are positioned at different heights on the base.
The 1157 is an ANSI-standardized bulb recognized in both the United States and Canada, meaning its physical and electrical specifications conform to a defined industry standard rather than a proprietary format.
Because the front and rear turn signal positions share the same bulb type on the Mack DM, a single 1157 bulb is interchangeable between both locations on the vehicle.