Number plate light loss of voltage

[cawthrm]

XF 2009. One of the rear number plate lights is out - bulb had blown. Changed the bulb, no joy. Checked voltage - no voltage on the bulb holder and tracing it back to the connector behind the boot trim, no voltage there either. Can anyone help with where it is fed from? The fuse descriptions in the manual actually don't mention any fuses related to any of the exterior lights, most strange. The sister number plate light which runs through the same connector has voltage and works fine.

[davidr]

I have heard of the wiring breaking where it is flexed by opening and closing the boot - maybe worth a look?

[cawthrm]

Thanks David, you may well be right. I have now rewired so both lights are fed from the one remaining live wire that is healthy. Remove the trim from inside the boot lid and it is the easily visible connector with black / white / blue / yellow wires. Anyone else doing this should check that no wire / component is overheating with carrying double the current, but mine appears to be fine. Bulbs are 5W.

I am still puzzled more generically - does anyone know where the headlights / sidelights / indicators and number plate lights are fused? As I mentioned previously they are not mentioned in the manual in any of the three fuse boxes in an XF.

[Rictus]

I have done some searching. The most common reason for number plate light faults is the boot loom as David says. As far as I know there is no specific fuse as the lights are protected by Field Effect Transistors (FET's). The FET's can detect overloads and short circuits and respond to heat generated by increased current flow caused by a short circuit.
On a normal conventionally protected circuit this would cause a fuse to blow. The FET's respond to the heat increase and disconnect the power supply to the affected circuit. When the fault is rectified or the FET has cooled, the FET will reset and operate the circuit normally. If the fault persists the FET will cycle, disconnecting and reconnecting the power supply.
You may be able to check for fault codes using a Jaguar approved diagnostic system.

(My thanks to Colin at jaginfo for this information).

[cawthrm]

Thank you gentlemen. Advice was correct. Subsequently the manual boot opener stopped working (still worked from the key fob or from inside the car, just not the button under the boot lip) and then the rear view camera failed. I replaced the piece of the wiring loom that runs through the hinge of the boot, a piece about a foot long and easy to connect once you've removed the boot lid trim. All now working again. Cost of the part is around £80.