Volvo 780 Back Up Light Bulb Size

The Volvo 780 back up light requires a P21W bulb size for proper installation and function within the rear lighting assembly. Data for the specified component covers the range from 1987 to 1991.

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
1987-1991	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 Volvo 780 uses the P21W bulb for the back up light across all listed model years, spanning 1987-1991.
The P21W is an ECE-standardized bulb type, meaning it conforms to European and international automotive lighting regulations rather than SAE standards used in North American specifications.
P21W bulbs operate on a 12-volt electrical system and draw 21 watts, which is typical for single-filament signalling applications such as reverse lights.
The P21W uses a BA15s bayonet base, where "BA" denotes a bayonet cap fitting, "15" refers to the 15mm base width, and the lowercase "s" indicates a single contact at the base.
Because the P21W is a single-filament bulb, it serves one lighting function only, distinguishing it from dual-filament variants such as the P21/5W, which would not be a direct substitute.
The BA15s bayonet mount requires a quarter-turn locking action to seat the bulb, and substituting a bulb with a BA15d double-contact base would result in an incompatible fitment for the Volvo 780.