The Mack Mid-Liner CS Series front and rear side marker bulb utilizes a 1891 size bulb for both locations. The replacement chart covers vehicle production spanning 1986 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 CS Series uses the 1891 bulb across all listed model years, 1986-1997, for both front and rear side marker positions.
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 itself rather than by a separate metal base with pins, which is a common trait of low-wattage marker and indicator bulbs.
The 1891 operates at 12 volts and draws 2 watts, placing it among the lower end of the power consumption range for incandescent automotive bulbs.
The 1891 carries ANSI standardization applicable in both the United States and Canada, meaning the bulb specification conforms to a recognized North American technical standard.
Because the front and rear side marker positions on the Mid-Liner CS Series share the same bulb size, a single bulb type services both locations across the entire model range covered by the specifications.
The T5 wedge form factor is widely used in marker, clearance, and instrument panel lighting applications, and the 1891 is a recognized fitment within that category.
The consistency of the 1891 specification across all twelve model years listed indicates no mid-cycle change in bulb fitment occurred for either side marker position during the production span covered.