The Mack DMC front and rear side marker bulb size specifications utilize 1891 bulbs for both locations on this truck model. A replacement chart covering 1981 through 1986 vehicle production years documents the bulb size data for these marker applications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mack DMC uses the 1891 bulb for both front and rear side marker positions across all listed model years.
The 1891 is an ANSI-standardized bulb, meaning its specifications are governed by a recognized North American standard applicable in both the United States and Canada.
It belongs to the T5 form factor, a miniature wedge-base bulb type commonly found in low-power indicator and marker applications on commercial vehicles.
The wedge base design means the bulb is held in place by tension from the socket contacts rather than by a bayonet or screw mechanism, which affects socket compatibility.
The 1891 operates at 12 volts, consistent with standard 12V automotive electrical systems.
At 2 watts, the 1891 draws very low current, a characteristic typical of side marker and indicator bulbs rather than primary lighting bulbs.
The front and rear side marker positions on the Mack DMC share the same bulb specification for the years 1981-1986, indicating no positional differentiation in bulb requirements.
Because both marker positions use the same 1891 bulb, a single bulb type serves the full side marker fitment for this vehicle across all listed years.
The T5 wedge form factor is not interchangeable with bayonet-base or screw-base sockets, so socket type must correspond to the wedge-base design when replacing this bulb.