Thanks very much for the replies.The Yahoo Emco CNC group seems to be spinning down.
I didn't do anything to the switch. I'm in Overland Park, KS (KC area). Bought the re-wired lathe from a used machine seller in Florida that had traded for it. The owner from whom my seller acquired the lathe had retrofitted it to control with Mach 3, which I know nothing about.
I'm not sure what "jumped" means, but I'd guess that what was done. Each of the three pairs of wires that connect to the key switch were/are simply twisted together. There is no switch (ahead of the spindle motor switch); plug the machine in, and it powers on.
My assumption was that the re-wiring was related to retrofitting for control by Mach 3, but now I wonder whether it might instead have been another way to put a Band-Aid on the contactor. I'll probably find out when I reconnect the switch. If it doesn't power on, then I'll have two nearly unused, very late version EC5 PC with apparently the same problem, although I suspect there are many different potential underlying causes for contactor failure. A question is what are the most likely causes for minty, late models.