just to clarify, that first set of 4 codes that you quoted was me looking up the codes from a general listing. Everything afterward is after I was directed by members here to a listing of the codes that is Porsche specific, so you can see how P1117 for the rest of the world and P1117 for Porsche are two very different things.
But I definitely get what you're saying regarding "interruption of signal". Guess it may be time to start tracing wires and connections...oh joy.
I do want to check the grounds myself, and particularly that grounding strap on the alternator. I've been told by two different technicians that they looked fine, but I want to be sure, and then start looking at what's likely to be a lot of 15 year old wiring. I'll also take a look at the ignition switch to be sure it was done right.