Diamond Reo C120 Back Up Light Bulb Size

The Diamond Reo C120 back up light requires a P21W bulb size for proper installation and function. Data for the specific component covers the range from 1992 through 1998.

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
1997-1998	P21W
1992-1993	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The P21W is the sole bulb type listed for the Diamond Reo C120 back up light across all specified model years.
The P21W operates at 12 volts with a 21-watt output, classifying it as a single-filament signalling bulb.
The P21W uses a BA15s bayonet base, which is a single-contact bayonet fitting with a 15mm collar.
The P21W is governed by ECE standards, meaning it is a regulation-compliant type used in European and worldwide automotive markets.
The single-filament design of the P21W means it serves one lighting function only, which in this context is the back up light.
The C120 back up light fitment is consistent across the 1992-1993 and 1997-1998 model years, all calling for the P21W.
The BA15s base designation indicates a non-indexed bayonet mount, meaning the bulb has no polarity orientation requirement during installation.