Typically contact or circuitry goes bad. Its not necessarily the traction control that is the issue, but rather the whole electronic throttle system in general. People have had good luck with getting a rebuilt throttle body, or whatever other sensor is at issue.
The larger problem, especially with '92 or '93 9000s is that techs have issues communicating with the electronics in the car with the diagnostic equipment. Which leads to not having a clear picture of what components are at fault, or not being able to recalibrate the system.
The nice thing about a '92 9000, is that you can pretty easily revert the electronic throttle components as well as associated electronics with cable throttle stuff from a '91 9000.
The reason is as follows, It's a very complex and over engineered system. When it came out the testing equipment wasn't up to the task of diagnosing it so most tech's that had to try and fix it hated it (me). The system is interwoven into many different systems too. You have TSC (traction control), ABS (anti lock brakes), and KDM (kick down motor), all wired togather sending signals and trying to work together.
yours might be a simple problem or cost more than the car is worth to fix. One thing I can tell you is that without at least a ISAT throwing parts at it is useless. All of the systems will need to be calibrated once you THINK you have it fixed (in fact calibrating it alone could fix it).
I've said it before and will say it again, I've sent very nice cars to the crusher just because if TCS issues and not wanting the headaches of keeping it running after selling it. When this system works it's a great system but it can be troublesome too.
Yesss the saabsite.com sells the TCS button kit. But be aware that it actually does very little only turning off Traction control until the car is started again.
Only useful for doing burnouts It does NOTHING in the way of turning off the TCS.. and it's infamous Limp Home.