How to disable the factory alarm?

[Per Lindgren]

Good People,

I have installed a 'Defa' aftermarket alarm system in my Audi today, but
there is a conflict with the factory alarm.

When I lock the car with the key, the factory alarm is activated (little
honk in the horn). Later, when I try to turn off the new alarm, it
grouds the door switch, because it has a feature that lights the
interior light for 30 secs when alarma is turned off. But because of
this, the factory alarm sees the earth connection from the other alarm,
and starts honking and flashing the emerency lights. So I will have to
disable the factory alarm. How do I do that?

TIA,

PerL
92 Cabrio 2.3E