Hi, Ontario members -- I was kind of thinking of Canada (as well as some parts of the U.*.) where it'* difficult to just pop in to parts stores and get free scans.
With regard to '96 plus vehicles (OBDII) what I plan to do at this point is to buy a handful of raw connectors that could be used to make up cables for any Bonnevilles (or compatibles) from '94 on, since they all start with the 16-pin J1962 socket (but of course the OBD protocol is different for the '94 and '95). So yes, I could make up missing or desirable cabling (but not a code reader) for say your '97+ cars. There'* lot'* of forum members to get the details and advice from -- which I would do. But if you want the complete code-reader, your lowest cost bet would be to get one from Harbor Freight (I think Bill Buttermore referenced it in a post a year or so ago) or from ebay.
In addition, as I mentioned, I'm planning to wire directly into an old computer and set up a diagnostic scanner (which is different than just a code reader -- you get codes, but you get lots of other data (voltages,etc)), that are handy when just the codes aren't enough.
In principle, this should work on all Bonnevilles (or GM compatibles) from '94 on, depending on software..
So.... I will make a cable, acquire some software and plug it all in to the serial port of my old computer. I should be able to scan both my '94 and '98. Again, Bonneville Club members have experience with this, and they will post-searched and pestered
I will post successful (I hope) results. Thanks for your interest, guys (and/or gals)!