[Gene Alvarez]

I think you disconnected the right connector for the thermo switch. Did your shop actually try replacing the relay (it's not cheap)? With a couple of pieces of wire and a light or ohmmeter someone could determine if the relay is OK. Maybe, if the relay cover comes off (I don't know) you could see if the contacts are stuck on and gently pry them apart. If the latter is the case, I would buy a new relay even though the old one might start working again for a while. Stuck relay sound more likely than a stray ground.
Gene