Mack RW Back Up Light Bulb Size

The Mack RW back up light bulb size is 1156, a specification applicable to this truck model. The replacement chart covers vehicle production years from 1985 to 1993.

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	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 RW uses the 1156 bulb for its back up light across the 1985-1993 model years.
The 1156 is an ANSI-standardized bulb recognized in both the United States and Canada.
It operates on a 12-volt electrical system and draws 21 watts.
The 1156 is a single-filament bulb, meaning it serves one lighting function rather than combining two, such as stop and tail.
It uses a BA15s bayonet base, which is a single-contact bayonet mount that locks into the socket with a twist.
The BA15s base is not interchangeable with the BA15d base, which features two contact pins instead of one, despite the two types sharing the same bayonet collar size.