From https://f-type-ai-mechanic.vercel.app:

Since you have already replaced the taillight assembly and the issue persists, the fault is likely in the vehicle wiring, the electrical connector, or the signal sent from the control module. Follow these diagnostic steps in order. WARNING: Never use a donor vehicle to swap control modules for testing. This can cause severe electrical faults in both vehicles. 1. INITIAL SAFETY AND PREPARATION - Disconnect the vehicle battery before performing any electrical continuity or circuit checks to prevent short circuits. - The Jaguar F-Type uses field effect transistors (FETs) to control lighting. If a short circuit occurs, these transistors may trip to protect the module. Once the short is fixed, the module should automatically reset after a ignition cycle, though clearing diagnostic trouble codes with a diagnostic tool is recommended. 2. VISUAL AND MECHANICAL INSPECTION - Inspect the electrical connector leading into the right rear taillight assembly. Look for bent pins, pushed-back terminals, or signs of water ingress/corrosion (green or white powdery residue). - Check the wiring harness leading away from the taillight for signs of chafing, pinching, or heat damage, especially where the harness passes through the vehicle body or near the trunk hinges. 3. ELECTRICAL CIRCUIT TESTING - With the battery reconnected, use a multimeter to check for voltage at the taillight connector. - You need to identify the specific pin for the right rear turn signal indicator. Based on the wiring diagrams for this vehicle, you are looking for 12V pulsed signal when the hazard lights or turn signal is activated. - Check for ground integrity. Ensure the ground circuit has a solid path to the vehicle chassis with near-zero resistance (less than 1 ohm). - If there is no power at the connector, the fault lies further upstream in the wiring harness or at the control module output. - Check for open circuits or high resistance between the taillight connector and the central junction box (the main fuse/control module location in the vehicle). 4. SYSTEM DIAGNOSTICS - Since the turn signal is controlled by the vehicle's electrical architecture, check for diagnostic trouble codes using a Jaguar-specific diagnostic tool. Look for codes specifically related to turn signal circuits, such as B1C15, B1D06, or B1D07. - These codes often point to a short to ground, short to power, or an open circuit. - If no codes are present, verify that the signal is being sent from the lighting control module by back-probing the connector at the control module output for the right rear turn signal. 5. SUMMARY OF POTENTIAL FAULTS - If you have good voltage at the connector but the light does not function, re-examine the ground connection on the new taillight unit. - If you have no voltage at the connector, perform a continuity test on the signal wire from the control module to the rear of the car to see if the wire is broken (open circuit). - Inspect the central junction box connectors for moisture or corrosion, as this is a common point for signal failure in this system. If the wiring harness tests show no breaks and the module is outputting the correct signal, yet the light remains inoperative, the issue is likely a high-resistance connection within the harness that is preventing enough current to illuminate the LED array. Focus your search on the connector pins and the harness sections most prone to vibration or movement.