The Mack Mid-Liner MS Series uses a 1891 bulb size for both front and rear side marker applications. 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 Mid-Liner MS Series uses the 1891 bulb for both the front and rear side marker positions across all model years from 1981-1997.
The 1891 is an ANSI-standardized bulb recognized in both the United States and Canada, meaning it conforms to a defined set of electrical and physical standards shared across those markets.
The 1891 bulb belongs to the T5 miniature wedge family. The T5 designation refers to a tubular glass envelope that is 5/8 of an inch wide, and the wedge base type means the bulb is held in its socket by the pinched glass base itself rather than by a separate metal cap.
The 1891 operates at 12 volts and draws 2 watts, placing it among the lower-wattage bulbs used in automotive marker lighting applications.
Because the same bulb type is specified for both the front and rear side marker positions, a single part number covers all four marker sockets on the vehicle.
The 1891 bulb specification remained unchanged across the entire 17-year production span of the Mid-Liner MS Series, indicating a consistent socket and circuit design throughout that period.