Bolted starter on, cleaned battery terminals and terminals on solenoid. Starts up great, have not seen the problem since and I have cranked it at sporadic intervals both hot and cold starts about 20 times or so.
After driving it a while my OIL light came on. So I let it set and checked the oil and it's almost full.
All of the wiring going into the firewall is old and brittle, I cracked the wire that runs to the oil sensor and there's about 1/16" of copper showing through. The oil light goes off when I unplug the wire from the sensor though, so I don't know if that means the wiring has current flow or not.
It just seems that it would be wiring rather than loss of oil pressure because of all the messing around with the wiring I did today, unless something coincidentally happened to the engine. Any thoughts?