Welcome!
As I understand it the Saab 9000 will need a code if the power is disconnected. There is no way around this; you will have to find the code.
There are possibly three ways.
1. If it is the original radio, a Saab dealer should be able to find the code for you.
2. Many radios, especially if they have ever been serviced after purchase, have the code scratched into the case by the repairer, or stuck onto a label. Pull the radio out and have a look.
3. Sometimes the code is written in the original documentation somewhere. If you still have any, give it close inspection.