Fiat 500X Courtesy Bulb Size

The Fiat 500X courtesy light utilizes 12961 and DE3423 bulb sizes for interior illumination. Data for 12961 and DE3423 covers the range from 2016 to 2021.

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
2021	12961
2016-2018	DE3423

Bulb Specifications

Description	Bulb Size
Philips part number. Miniature wedge bulb (T10) with W2.1x9.5d base. 12V, 5W.	12961
ANSI standard (US & Canada). Festoon bulb, 41mm length, end-cap contacts. 12V.	DE3423

Other Locations

Additional Notes

The Fiat 500X courtesy bulb specification splits across two distinct bulb types depending on the model year, with the DE3423 festoon bulb assigned to 2016-2018 and the 12961 wedge bulb assigned to 2021.
The DE3423 is an ANSI-standardized festoon bulb recognized across the US and Canadian markets. It measures 41mm in length and makes electrical contact through end-cap terminals at both ends of the bulb body.
The 12961 is a Philips part number designating a T10 miniature wedge bulb with a W2.1x9.5d base. It operates at 12V and draws 5W. The wedge base design relies on the bulb's own glass envelope and wire leads to form a friction fit within the socket, with no separate metal base or end caps.
The festoon and wedge formats are physically and electrically incompatible with each other. The DE3423 seats into a spring-clip festoon socket, while the 12961 inserts into a wedge-type socket, meaning the two bulb types are not interchangeable across the Fiat 500X model years listed.
The 12V operating voltage is shared by both bulb types, which is consistent with standard automotive electrical systems. However, the wattage rating is confirmed only for the 12961 at 5W, placing it in the low-current range typical of interior courtesy lighting.