Screw Drive?
Belt tension switch.
Stop switch under the unit near the base support.
Pan switch.
Some weird unmarked keyswitch on the run panel?

Roped Unit?
Slack rope switch.
Pan switch.
Low oil switch.
Limit switch.

Never heard of a “motor stop switch” either. Thermal maybe? Did you ever see this platform unit run? Maybe some “option” jumper not in place. Prints I think would show it if it were an optional feature, but you never know.