Strange problem with lights on warning buzzer

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My "lights on warning buzzer" doesn't work. The lights in the coupé are turning on when I open the door, so the door switch should be working alright.

I have checked the buzzer under the fuse panel, and it's working. The "door open warning buzzer" works, but only if I remove fuse 30 (read below) from the fuse panel. The fuses seems to be OK, the door switch seems to be ok, and the buzzer itself seems to work. But it won't give a sound if I leave lights on. Any help would be appreciated!

Fuse 30:
map reading lamp, vanity mirror, glovebox light, lights on warning buzzer, indicators, rear view mirror adjustment, electric window one touch operation, rear electric windows relay