Doug, I have had this 5er 10 years and no one has been in that air conditioner until I changed the card about two years ago. Before 2008 maybe. So that yellow has been connected for 10 years, I think. It is possible that it was hanging there and I hooked it up to the new board but I don't think so. I'm usually more careful than that. I'm not sure what a spade is but my wire had what I call a female wire connector which slides on to the male wire connector marked yellow on the board. I am sure that the whole system worked that way for some period of time. I think that yellow wire was connected when the unit was built. I have two ccc tstats because I do. I really don't remember how I got the second one. As you may have gathered I've been a shade tree mechanic since 1959 and I help guys out at RV parks. I often end up with some extra parts.
I think Imgoin4it had the same situation I had only he had a whole new air conditioner while I had a new motor and board. I'm guessing that something in the stat makes that yellow wire cause a problem with late model motors and boards.
Anyway I'm happy I found you guys. I don't think it would ever have occurred to me to disconnect that wire without this web site.