Mack DMC Back Up Light Bulb Size

The Mack DMC back up light bulb uses a 1156 size bulb for this model. The replacement chart covers vehicle production years spanning 1981 to 1986.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1984-1986	1156
1981-1982	1156

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

The 1156 is the sole bulb type specified for the back up light position across all listed model years of the Mack DMC.
The 1156 bulb follows the ANSI standard, meaning it conforms to a defined North American specification recognized in both the United States and Canada.
It is a single-filament bulb, which means it serves one lighting function only, as opposed to dual-filament bulbs that handle two functions such as running and brake light duties.
The 1156 uses a BA15s bayonet base, a single-contact mount where the bulb is inserted and twisted to lock into place.
The bulb operates at 12 volts and draws 21 watts, consistent with standard automotive electrical systems of that era.
The Mack DMC used the 1156 bulb across the 1981-1982 and 1984-1986 model years for the back up light position.
The BA15s base designation indicates a single-contact bayonet fitting with a 15mm base width, which is not interchangeable with the BA15d double-contact variant despite sharing the same physical base size.