It appears to have been the plunger switch all along. I tried but had no success by-passing the switch and getting the fan operating, but I did connect the lead and ground wires to the fan motor directly to the battery
, and the motor is clearly not the problem. Fan-Tastic was great, and they have a new plunger switch in the post already. If the new plunger switch doesn't solve the problem, I suppose I'll have to try to sort out the intake/exhaust switch, but I'm relieved to know the problem isn't the motor. Now I can go back to enjoying retirement with my fiddle -- not a multimeter -- in hand!!! But I enjoyed trying to sort out the problem and really appreciate all the excellent guidance the forum folks provided. Thanks yet again.