Mack RD Back Up Light Bulb Size

The Mack RD back up light bulb uses a 1156 size bulb for this truck model. The replacement chart covers vehicle production years spanning 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 RD uses the 1156 bulb for the back up light position across all listed model years, spanning 1981-1997.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical specifications are defined by a recognized North American standard applicable in both the United States and Canada.
This bulb operates on a 12-volt electrical system and draws 21 watts, which is typical of incandescent single-filament automotive bulbs used in non-lighting signal applications such as reverse indicators.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width. The single-contact design corresponds directly to the bulb's single-filament construction.
Because the 1156 is a single-filament bulb, it is not interchangeable with visually similar dual-filament variants such as the 1157, which shares the same bayonet base style but carries two contacts and two filaments for separate functions.