Cadillac STS License Plate Bulb Size

The Cadillac STS license plate light requires a bulb size of 12961 for proper installation and function. Data for 12961 bulbs covers the period from 2005 through 2011.

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
2010-2011	12961
2005	12961

Bulb Specifications

Description	Bulb Size
Philips part number. Miniature wedge bulb (T10) with W2.1x9.5d base. 12V, 5W.	12961

Other Locations

Additional Notes

The Cadillac STS uses the 12961 bulb for its license plate position across the 2005, 2010, and 2011 model years.
The 12961 is a Philips part number designation for a miniature wedge bulb in the T10 form factor.
T10 refers to the bulb's tubular shape with a width of 10 millimeters, a standard sizing convention used across the miniature bulb category.
The 12961 operates at 12 volts and 5 watts, which is typical for low-draw auxiliary lighting positions such as license plate illumination.
The base type is W2.1x9.5d, a wedge-style base where the plastic body of the bulb itself acts as the retaining mechanism rather than a separate metal base or bayonet fitting.
The W2.1x9.5d designation indicates a wedge base with a 2.1-millimeter wire contact width and a 9.5-millimeter insertion depth, which governs physical fitment into the socket.
Any replacement bulb intended for this position must match the W2.1x9.5d base specification to seat correctly and maintain electrical contact in the Cadillac STS socket.
The T10 wedge format is widely produced by multiple manufacturers, meaning the 12961 Philips number represents one sourcing option within a broader pool of electrically and physically equivalent bulbs sharing the same base and ratings.