Thanks for that advise. I'm thinking the same. I'm just not familiar with the system. I wish I had the Helm book or a parts truck to tear into and explore. I didn't get the fan installed today like I had hoped. That will make it more obvious if the vent blend is working. If that is also not working I'm buying a new control head first and see what that does. Could be the one I got at the junk yard is actually junk!
I just liked the idea of a GM unit, even if used, over going with the replacement part. Also, it would be quite a coincidence if while my heat system was out of use these parts failed when all it needed was a new fan switch and while replacing the control head busted it's mount clips... which led to adapting '96 up unit.