Fiat 124 Back Up Light Bulb Size

The Fiat 124 back up light utilizes P21W and 1156 bulb sizes for the lighting components. Data for the specific bulbs covers the period from 1976 through 1983.

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
1976-1983	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 1156 is the sole back up light bulb size listed for the Fiat 124 across all model years covered in the specifications, spanning 1976-1983.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical characteristics conform to a defined North American standard recognized in both the United States and Canada.
As a single-filament bulb, the 1156 serves one lighting function per unit, which is consistent with its application in a dedicated back up light circuit.
The 1156 uses a BA15s bayonet base, a single-contact bayonet mount with a 15mm collar. The "s" designation indicates a single contact pin, distinguishing it from the dual-contact BA15d variant.
The 1156 operates at 12 volts, which aligns with the standard 12V electrical systems found in passenger vehicles of this era.
At 21 watts, the 1156 falls within the typical power range for incandescent automotive signal and utility lamps, producing a moderate level of output suitable for reverse lighting.
Because the BA15s base accepts only single-contact bayonet bulbs, substituting a dual-contact variant such as the 1157 or a BA15d-based bulb would result in an incompatible fitment for the Fiat 124 back up light socket.