Mack U License Plate Bulb Size

The Mack U license plate light utilizes a single 1891 bulb size for illumination across all recorded vehicle configurations. Available technical data for the specified lighting component covers the production range from 1981 to 1989.

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
1981-1989	1891

Bulb Specifications

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

Other Locations

Additional Notes

The Mack U uses the 1891 bulb for its license plate lighting across all model years represented in the specifications, spanning 1981-1989.
The 1891 is classified as a T5 miniature wedge bulb, where "T5" refers to a tubular bulb shape with a width of 5/8 of an inch.
The wedge base design means the bulb is held in place by the socket gripping the glass envelope directly, with no separate metal base or pins involved.
The 1891 operates at 12 volts and draws 2 watts, placing it among the lower-wattage miniature bulbs used in automotive applications.
The 1891 carries ANSI standardization recognized in both the United States and Canada, meaning the bulb designation refers to a consistent specification across both markets.