+1 for a gauge...
Idiot lights either work or don't, and there's no way for you to know for sure what the pressure is without a gauge.
I'd hook up a gauge, turn the kill switch to off, crank that hoebag over and read the pressure, if its coming up at all I would replace the switch or pull it out and throw it against the wall a few times to try and unstick it, then pop er back in and see what happens. Still no go, get a new switch. Never had on apart but my guess is its a ball and spring switch and with old crudded up oil from being sitting while you rebuilt your motor, the ball is probably stuck.