I don't know about the dash switch, but its a pretty simple thing to check. However, when the button is depressed you can hear and audible click.
I have notcied the manifold does get warm when the tractor isn't running so I'm inclined to suspect the solenoid (or the glow plug) is at fault. However, once you get old Brutticus started, the ammeter always reads the battery is somewhat discharged(likely 'cause draws a pile of amps) and after running, the guage reads normal. So I don't think the pre-heater system is drawing any juice out of the charging system (with the engine running and warm , I don't see the pre-heater system in operation)while the engine is running.
When I get the chance, I'll check the aforementioned components in detail.