"after a few miles the light comes on, blinking and then on full time so I pulled over to see what was up.Now to make a long story short, the guy that did the service did not tighten the drain plug and all the oil drained out So now maybe I have this bass ackward Low oil ? and no, it didn't have a pressure gage"
You have to have oil to pump, to generate pressure.
Oil can also be to the full mark, but if the pump fails, the light comes on. It's a PRESSURE Switch!