Mack MH front and rear side marker bulbs use 1891 bulb size specifications. The replacement chart covers 1983 to 1994 vehicle production years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mack MH uses the 1891 bulb for both its front and rear side marker positions across the 1983-1994 model years.
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 1891 bulb is held in place by the socket gripping the base of the glass envelope 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 on the Mack MH, a single bulb type services all four side marker locations on the vehicle.
The T5 wedge form factor is shared by several bulb numbers, and substitution with a physically similar bulb of a different wattage or voltage rating would fall outside the specified requirements for this vehicle.