Diagnostic help
WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
The control module output can be activated and the input from the switch read with the diagnostic tool.
If the indicator lamp goes on when the control module output is activated, the fault is probably located between fuse 17 and pin 28 on TWICE.
If the indicator lamp does not go on when the control module output is activated, the fault is probably located in the relay (511) circuit to the seat-belt warning (64RL/RR).