Mack Mid-Liner MS Series Headlight Bulb Size

Additional Notes

• The Mack Mid-Liner MS Series (1981-1997) was offered with three distinct headlamp configurations: a 2-round-headlamp setup, a 4-rectangular-headlamp setup, and a 4-round-headlamp setup. Each configuration uses a different set of bulb sizes, and the correct fitment is determined entirely by which headlamp arrangement is present on the vehicle.
• All headlight bulbs specified for the Mid-Liner MS Series across all three configurations are sealed beam units conforming to ANSI standards recognized in both the United States and Canada. In a sealed beam design, the reflector, lens, and filament are fused into a single unit, meaning the entire assembly is replaced rather than an individual bulb.
• The H6024 is a 7-inch round sealed beam unit operating at 12V. It serves as both the high beam and low beam bulb on vehicles equipped with the 2-round-headlamp configuration, making it a dual-function unit across all years covered by the specifications.
• The H5001 and H5006 are both round sealed beam units used in the 4-round-headlamp configuration. The H5001 is a 4-inch square sealed beam designated for high beam duty, while the H5006 is a 5.75-inch round sealed beam designated for low beam duty. These two types are not interchangeable with each other despite sharing the same headlamp configuration.
• The 4-rectangular-headlamp configuration uses 4x6-inch sealed beam units for both high and low beam positions. The H4651 is specified for high beam use across all years, while the low beam position is filled by either the H4652 or H4656 depending on the model year. The H4652 is described as a variant of the H4651, though all three are distinct ANSI part numbers and are not interchangeable across beam positions.
• The low beam rectangular bulb for the 4-rectangular-headlamp configuration is not uniform across all years. The H4656 is specified for 1981, 1986-1988, 1994, and 1997, while the H4652 is specified for 1982-1985, 1989-1993, 1995, and 1996. Both are 4x6-inch rectangular sealed beam units at 12V, but they carry different ANSI designations and are not listed as interchangeable within the specifications.
• All six bulb types listed across the specifications operate at 12V. This is consistent across every headlamp configuration and every model year covered, indicating a uniform electrical system voltage requirement for the headlighting on the Mid-Liner MS Series.
• Because all units are sealed beams, physical size and ANSI designation together govern correct fitment. A 4x6-inch rectangular unit from the high beam position cannot substitute for a round unit in another configuration, and vice versa, even though all units share the same operating voltage.