Luggage Compartment Switch, Lighting: Function
WARNING: This page is about a different car, the 2006 Saab 9-5. However, it is still accessible from the selected car via links, so may be relevant.
A continuous pulse width modulated (approx. 3.5%) voltage is supplied from the control module via a 1 kohm pull-up in TWICE to the switch. By checking this voltage on the control module input, the control module can monitor whether the boot lid/tailgate is opened while the alarm is armed.