I would first inspect the disconnect switch. Use a test light and check that power is going into the switch, close it and see that power is coming out the other side. If not the problem is in the cut off device. Has the ignition switch ever given you any trouble? I would use the test light and a schematic showing the switch and the connections. Ground the test light, locate which lead comes from the battery and insure you have voltage to the ignition switch. If you do, turn the switch on and see if you have power coming out the other side. If not you probably have a switch problem. Also check all the connections to see if they are tight and clean from corrosion. Just a WAG, but I am thinking you battery cut off switch is the problem.
