Fiat 500L Tail Light Bulb Size

The Fiat 500L tail light requires a P21/5W bulb size for proper installation and function within the rear lighting assembly. Data for the specified bulb covers the production range from 2014 through 2019.

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
2014-2019	P21/5W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Dual-filament signalling bulb with BAY15d bayonet base. 12V, 21W/5W.	P21/5W

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Additional Notes

The Fiat 500L uses the P21/5W bulb for its tail light across the 2014-2019 model years.
The P21/5W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe regulatory framework used in European and worldwide automotive lighting applications.
This bulb type carries a dual-filament design, with one filament rated at 21 watts and a second rated at 5 watts, allowing it to serve two distinct lighting functions within a single housing.
In tail light applications, the lower 5W filament typically handles the steady running light function, while the higher 21W filament activates for braking signals.
The P21/5W uses a BAY15d bayonet base, which is an offset twin-pin mount. The two pins are positioned at different heights, making the base directionally keyed so the bulb can only be inserted in one orientation.
The BAY15d base is not interchangeable with the BAY15s single-filament bayonet base, as the latter carries only one filament and a symmetrical pin arrangement, making it electrically and physically incompatible with dual-filament sockets.
The bulb operates on a 12-volt electrical system, which is standard for passenger vehicles of this type.