A4 Lights On Buzzer

[fairstep]

I am a new member, and hope someone can help me, cos its driving me mad!!!
The lights on warning buzzer does not normally work. However, if I leave the drivers door open while I insert the key and start the car, the warning works if I then turn the lights on and withdraw the key, and the red light on the door also comes on.
If I start with the drivers door closed, the warning does not sound, and the red light on the drivers door does not light up when the door is opened.
I removed the door lock from the csar snd the microswitch seems to be working OK
The car is a 1999 Audi A4 1.8 sedan, and has only done 27000 kms.
Any ideas please?