If it is like my switch, and I think it is, the bezel will unscrew to remove the switch.
The diodes inside the rectifier may also be a problem. A faulty diode will allow current from the battery to drain back into the alternator, killing the battery.
Is the charging system working? These tractors have rather weak charging systems, so lots of starts will run them down.
Check with a volt meter at the battery to be sure it's charging, and an ammeter to see if it's draining. Checking for a battery drain with an ammeter will eliminate any guess work as to the point of problem, as you can eliminate one thing at a time till you find the culprit.