Mack RW License Plate Bulb Size

The Mack RW license plate bulb uses a 1891 size bulb for this truck model. The replacement chart covers vehicle production from 1985 to 1993 with corresponding bulb size data.

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
1985-1993	1891

Bulb Specifications

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

Other Locations

Additional Notes

The 1891 bulb is the sole license plate bulb size listed for the Mack RW across the 1985-1993 model years.
The 1891 is classified as a miniature wedge bulb, using the T5 designation, which refers to a tubular glass envelope roughly 5/8 of an inch wide.
The wedge base design means the 1891 requires no separate metal base or socket pins, as the glass envelope itself forms the electrical contact when inserted into a wedge-style holder.
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, meaning its physical and electrical characteristics conform to a defined specification recognized in both the United States and Canada.
Because the 1891 is an ANSI-standardized part, it is produced by multiple manufacturers and is widely available as a direct replacement without modification to the socket or wiring.
The T5 wedge form factor is shared by several other bulb numbers in the miniature wedge family, though voltage and wattage ratings differ between them, making those alternatives non-interchangeable with the 1891 despite physical similarities.