One thing to keep in mind when checking voltage at any power terminal is to use a 12 volt test light. because even if you have 12 on the volt meter does not mean that you will it in the on position, as there is draw on it. All of these tests will tend to lead to poor connections as opposed to a actual failure in the switch.
I have now had my JM254 for a year, most of which just it has been stored out in the elements. My starting issue was a poor corroded + terminal on the starter itself. They must stored completed Jinmas outside in china.
The other posibility is the clutch safety switch by your left foot. Mine actually broke/bent on the bracket, because the switch bottomed out before the clutch pedal. (I was doing alot of loader work and the next time I went to start it, it was dead). There are two wires leading to this switch, tie them together and try it. Keep in mind you can now start in gear (dangerous).
I love my JM254. Up in the Yukon we are now full winter, -15c and snowing.