It's never had a single problem and now this all of a sudden. Fuse box was replaced when I got it a few years ago.I hear you brother, You can try checking the voltage before it does into the ignition switch. These 40 are old but once you get all the bugs out, they are very dependable. It may need a lot of cleaning of contacts and terminals, visual checks on the wiring. The fuse box is another area of interest but once start checking voltages you will have a better idea what to do.
That is strange. Do you have spark?. Sometimes these things end up being something really simple like the centre high tension dizzy lead or the little graphite button inside the centre of the dizzy cap has fallen off.New coil, points, condenser, wires, ballast resistor, ignition switch and still nothing.