Thanks, so far I have not been able to find a battery disconnect that will work on this tractor. The battery posts are way too close the the sheet metal side enclosures but I'll keep looking. I will look into the alternator issue as well.
Put your disconnect on the negative / ground terminal of the battery. If the switch, or negative terminal contacts the sheet metal, it’s no big deal, it’s already electrically contacted to the sheet metal through the neg ground cable.
Just make sure that when the switch is open, the “battery side” of the switch isn’t making contact to the sheet metal and bypassing the open switch or battery can still drain.
Using the ammeter function across the open switch, or from a disconnected battery cable to the battery terminal, will tell you how much current is leaking. (Hopefully less than your meter can measure)
Pulling fuses until you find the one that stops the leakage can also be useful.
[Additional info: the voltage across the open switch should match the voltage across the battery terminals, because electrically, although no current can flow through the open switch, the negative cable should have +12v on it , as as the voltage is continuous from the battery positive terminal through the leaking device. No current flow = no voltage drop. Unless it’s a leaking diode in an alternator or solid state relay, then things can measure weird as the meter’s characteristics come into play. But I digress. ]