Ignition barrel not illuminating

The ignition barrel has stopped illuminating in my 2001 D2 (it used to come on with the interior lights when the doors were unlocked, with the remote fob).

even though I have changed the bulb and there is a 12v supply to the bulb itself, it still doesn't light up.

Any assistance would be appreciated.

Thanks,
Nick

If you have a supply and the bulb is ok then it must be a faulty return to earth.