The central warning system on these cars comes straight from aviation, DeHavilland, to be exact.
On most modern airliners when a problem is noted a yellow "caution" or red flashing "warning" light on the top of the glare shield [dashboard] will illuminate telling you to look at a flat panel display mounted on the center of the instrument panel where the problem is spelled out. If it is an electrical problem, the computer that runs the planes systems has already isolated the bad bus or generator, and you need only write the problem up in the maintenance log.
Porsche decided that it would be easy to copy this system and install it in a car. It is a very good idea, since it gets the attention of the owner. This system only works when something is really wrong, so you don't get used to seeing it on a regular basis. Frankly, considering several females I have dated, I think that Porsche should have installed an engine disable function should coolant temperature run too high or oil pressure run too low.
[That's not an indictment of the female, just certain members of that group~]
In any case, there is probably a wiring issue. What fuse protects the CIWS? Is it the same as the cruise control? For your year, is the CIWS system on the same plug on the fuse panel as the cruise? Check there.
928 SPECIALISTS ONLINE STORE - 30,000+ 928 Parts - 928 SUPERCHARGER KITS! has all the relays and fuse configurations on their website.
If you can't figure it out, you should consider removing the fuse for the cruise control.
N