Mack Mid-Liner MS Series Back Up Light Bulb Size

The Mack Mid-Liner MS Series back up light uses a 1156 bulb size for this lighting component. The replacement chart covers vehicle production spanning from 1981 to 1997.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1981-1997	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The Mack Mid-Liner MS Series uses the 1156 bulb for the back up light position across all model years from 1981 to 1997.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical specifications are governed by a recognized North American standard applicable in both the United States and Canada.
The 1156 operates on a 12-volt electrical system and draws 21 watts, which is typical for incandescent automotive signal and reverse lighting applications.
The 1156 is a single-filament bulb, meaning it serves one lighting function only, which is consistent with its dedicated use as a back up light.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width. The single-contact design is directly related to the single-filament construction.
The BA15s base type is not interchangeable with the BA15d base, which is a dual-contact bayonet fitting used on two-filament bulbs such as the 1157. Substituting one for the other is not possible without a socket modification.
The 17-year span of consistent 1156 fitment on the Mack Mid-Liner MS Series indicates a stable back up light socket design throughout the production run of this model.