Advice "Safety" First
Find out what kind of rigamarole "a thrown code" means as far as re-setting. Some vehicles need to go to the dealer $$$$$$$$$$
See if you can get your hands on a xerox of the GM Technical Service Bulletin dealing with ECU / Alternator issues. I'm a little far from a dealer. But tell the service manager the truth "It's for someone who does not live in the USA and -desperately- needs the TSB :)" One question for the service manager "Does my system send a FIELD REPORT to the ECU?"
You are correct, loss of sense lead will result in a default voltage setting. The earliest Delco 10SI had a ludicrously high 16.4 volt default. Your comment of course makes sense.
I need to see a picture of the rear (slip ring end) of your alternator. Another favor to ask of your dealer parts department. Or at least get the factory Delphi part number for your alternator. I can do an online search from there.
Botched diagnosis is out of the question so please pardon my caution doing this.
