I thank you mike

I went to 'flaps' and found many an oil pressure switch. some w/ one, two and three terminals, different threads and activations pressures. I choose a (carquest # PS-133) 1/8'' npt, pipe thread, dryseal, switch which states term A to gnd. term B opens @ 3-9 psi N/C, term C closes @ 11 psi N/O. ''Also used simultanouesly as an electric choke heater switch''. used on AMC, Chrysler, GM, Ford, Chevrolet and others.
It's now pretty clear.

Gooday
Caroline & Jim
& Lucinda our 3104
51-3100 inliner @ 4655
small wheel moves by fire and rod,
big wheel moves by the grace of god,
every time that wheel turns round,
bound to cover just a little more ground.