The Mack MR front and rear side marker bulb size is 1891 for this truck model. Replacement bulb specifications in the chart cover vehicle production from 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 MR uses the 1891 bulb in both its front and rear side marker positions across all model years from 1981-1997.
The 1891 is classified as a miniature wedge bulb, meaning it uses a wedge-style base rather than a bayonet or screw base, and seats directly into a compatible wedge socket without a separate metal cap.
The T5 designation refers to the bulb's tubular envelope, which is 5/8 of an inch wide, making it one of the smaller bulb forms used in automotive lighting applications.
The 1891 operates at 12 volts and draws 2 watts, placing it among the lowest-wattage bulbs in standard automotive use, consistent with the low-intensity requirements of side marker lighting.
The 1891 conforms to ANSI standards recognized in both the United States and Canada, indicating it meets a shared North American specification for electrical and photometric performance.
Because the front and rear side marker positions on the Mack MR share the same bulb type, a single 1891 bulb serves as a direct replacement for either location on the vehicle.