Have you checked the switch? It is a 3 position switch, 1 for on all the time, 2 for off all the time and 3 for operated by the door/MFU.
The way it works is with the light selected to door operation, it is connected to the MFU (Multi Function Unit). When you open a door or unlock a door with the remote, the MFU gets a signal, either from the remote or from the earth pin switch near the door hinge.
This triggers the MFU to reduce the resistance on the earth line to the light and the light illuminates. After a period of time the MFU will then increase the resistance on the earth line and the light will begin to dim.
Eventually the resistance will be high enough to cause the light to appear extinguished but if you fit an LED type light it will still glow as there is always a residual current as it is not truly open circuit.