The Mack MC front and rear side marker bulbs both utilize a 1891 bulb size specification. The replacement chart covers vehicle production spanning 1981 to 1991.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mack MC uses the 1891 bulb size across all listed model years, 1981-1991, for both the front and rear side marker positions.
The 1891 is classified as a miniature wedge bulb, designated T5 in the tubular bulb sizing system, where the number indicates a width of 5/8 of an inch.
The 1891 operates at 12 volts and draws 2 watts, placing it among the lower-wattage bulbs in automotive lighting applications.
The 1891 conforms to ANSI standards recognized in both the United States and Canada, meaning it meets a standardized set of electrical and physical specifications shared across North American markets.
The wedge base design of the 1891 relies on the bulb's glass envelope and wire leads to form the electrical connection, with no separate metal base or pins involved.
Because the same bulb number is specified for both the front and rear side marker positions across all listed years, the two positions are served by a single interchangeable part on the Mack MC.