Mack DMM front and rear side marker bulbs utilize a 1891 bulb size specification. The replacement chart covers vehicle production spanning 1981 to 1997.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mack DMM uses the 1891 bulb in both its front and rear side marker positions across the full 1981-1997 model range.
The 1891 is classified as a T5 miniature wedge bulb, a designation that refers to its tubular glass envelope measuring 5/8 of an inch in width.
The wedge base design means the bulb is held in place by the socket gripping the base of the glass directly, with no separate metal base or pins involved.
The 1891 operates at 12 volts and draws 2 watts, placing it among the lower-wattage bulbs used in automotive marker lighting applications.
The 1891 carries ANSI standardization recognized in both the United States and Canada, meaning its electrical and physical specifications conform to a defined industry standard in both markets.
Because the same bulb number applies to both the front and rear side marker positions, a single bulb type serves all side marker sockets on the vehicle.
The T5 wedge form factor is a common fitment in low-current indicator and marker applications, and substituting a bulb of a different base type would not be compatible with the wedge socket used in these positions.
At 2 watts, the 1891 draws minimal current, which is consistent with its role as a marker lamp rather than a primary illumination source.