SO Just to tie a bow on this, my problem was indeed due to corrosion. Just as a psa, this tractor,as described, had no power to the starting circuit with a perfectly fine battery correctly installed. Now according to the electrical schematic and the description and the function of the thermistor, when the key is in the run position,it has no role to play. It isn't until you try and actually start the engine that the thermistor can be the problem. If your seeing the symptoms of there is no battery installed even though it is you probably have a corrosion issue somewhere in your electrical.
I checked the locations where you should be receiving battery voltage at all times, ie key switch in off position (key switch,light switch,turn sig switch,alternator, starter ,fuse 1,fuse 2,fuse 3,K1 K4 and K7 relays). All checked out fine for voltage except fuse three where the contacts in the fuse holder was badly corroded. I then performed the diagnostic on all the relays to check their proper function (all passed). I then checked for the proper function of my switches. key switch and light switch checked good, turn sig switch failed.
After that, I placed the key switch in the run position to verify "switched" power,and thats where numerous failures were happening. I was getting very low to no voltage beyond the the key switch. Knowing that I was getting the proper current supplied to the switch I again consulted the schematic. In accordance with operation of the start switch there are 4 operating positions (accessory,off,run,start) with seven points of contact. Contacts 1-2 receive constant voltage(key in off position), 3-5 are energized when the key is in the run position, 5-6 are energized in the start position, and 7 is accessory.
I made a jumper wire so that each contact could be tested individually and found that contact 5 was where my voltage drop was occurring. SInce the key switch passed it's diagnostic along with the fuses and relays within the start circuit the only remaining suspect was the wiring harness itself.
SO, I started ringing out (continuity check) each wire that received power from the #5 contact with the key switch in the run position. Just from a visual Inoticed many of the terminal connecters had a dull grayish color and had pitting. So I replaced all the ones that were not nice and shiny and voila she fires up with no issues. even all the lights work now and I reintegrated all the safety features that had been bypassed by the previous owner who prolly thought they were the cause of his issues with the tractor.
