Mack MH License Plate Bulb Size

The Mack MH license plate light requires a single 1891 bulb size for proper illumination of the rear vehicle identification area. Available data for the specified component covers the production span from 1983 through 1994.

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
1983-1994	1891

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Miniature wedge bulb (T5). 12V, 2W.	1891

Other Locations

Additional Notes

The Mack MH uses the 1891 bulb for its license plate light across all listed model years, spanning 1983-1994.
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 has no metal pins or bayonet fittings. Instead, the glass envelope itself acts as the base, held in place by tension within the socket.
The 1891 operates at 12 volts and draws 2 watts, placing it among the lower-wattage bulbs used in automotive applications, consistent with the minimal illumination requirements of a license plate light.
The 1891 carries ANSI standardization recognized in both the United States and Canada, meaning the bulb conforms to a shared North American specification rather than a manufacturer-specific or regional standard.
Because the 1891 is a standardized ANSI type, replacement bulbs from different manufacturers are generally interchangeable as long as they carry the same 1891 designation and conform to the T5 wedge form factor, 12V rating, and 2W rating.