I know nothing about 968's but have had a radiator switch fail twice on the 924. The first time, it failed in the on position and the fan ran all the time even with the ignition turned off (but at half speed). The second time (Yesterday) caused the engine to overheat.
I notice that you have two fans, so I would not know how to test what is faulty. There must be a thermo switch controlling the second fan. If you can get hold of a wiring diagram, you might be able to work it out.
Sorry, I can't help any further.
