if you leave the on/off switch in the on position and hook up the ground wire the engine turns over,
Larry-From what you are saying, the Floor switch is burnt out(or stuck on!)
My truck will turn over with the ignition(key) on or off(stepping on the floor switch),but will not start unless the ignition(key) is turned on.
If yours turns over with the ignition(key) on and you ground it, that sounds like the floor switch is stuck.