I recently had some bad luck with my QA-42A. Wet snow froze & ice chunks caused the spirol pin in the drive shaft to break. While replacing the pin, I noticed one of the quick-attach pins on the mounting bracket was broken off, so I had that replaced. Since it was just like new again, and since Santa didn't bring me new Vredestein 5-ribs for the front of my 782, I bought a pair from Miller Tire. Got them mounted just in time for a new snowfall and (wait for it...) the tractor wouldn't start. By now I'm starting to get a complex! I manually shorted across the solenoid and it spun the starter, so it was time to remove the fuel tank to access the ignition switch for trouble shooting. (First, I checked for 12V at solenoid when switch was turned to "start" position - nothing there.) After removing the switch and checking the functions with ohm meter and wiring diagrams from this forum, I discovered very eratic and intermittent functions. There was some corrosion on and around the contacts on the back of the switch,so I cleaned it all up with my Dremmel and a little wire brush, but it didn't change anything. Apparently there are issues inside the switch. The moral of this long story is that we are really fortunate to have this forum providing access to wiring diagrams, knowledge sharing, parts-lookup, and parts for our old tractors. Thank you Charlie!
(And for anyone who's never ordered any parts from CC Specialties (see sponsor button above), the service is amazing - I'll have my new switch in hand by mid-week, without having to drive 25 miles to a "local dealer and hope they have it in stock.)