Here's the wiring diagram. When the Central Junction Box Control Module receives a voltage signal from the brake pedal switch it outputs Power to the Right Rear brake lamp (on Pin 33 of the C3BP01F wiring connector) on the GY-VT wire.

 See if there's Power on that wire when the brake pedal is pressed at the Lamp Cluster wiring connector.

If not, maybe backpin that GY-VT wire right at the C3BP01F wiring connector and see if it's outputting Power when the brake is pressed.

 Should be the GY-VT wire on this connector:

 I don't know Jaguars but usually you'd start by doing a full system scan to check for circuit codes on these BCM/LCM controlled lighting systems because there aren't any fuses between the module and the lamps so the module has the ability to shut down the circuit because of high/low voltage and sometimes it won't turn the circuit back on until the code is cleared.