Glad to hear you got the ignition wiring figured out
Did you make any changes to the alternator harness and cab harness to hook up the ammeter in the gauge cluster? If you
have not yet made any changes to that part of the wiring, but
did add the black wire for the ammeter to the engine harness, I believe that would create a situation that would result in a battery drain. With that added black wire, you will now have constant power going to one leg of the ammeter (as it should). But if you haven't changed the cab/alternator wiring yet, the other leg of the ammeter would end up connected to the #4 terminal on the voltage regulator. And that terminal should only be powered when the ignition is on. But with the other side of the ammeter hooked up, it would feed power through the meter and keep the regulator/alternator energized all the time, draining the battery. If this is the case, simply leaving that added black wire disconnected from the starter solenoid (and taped up so it won't short against anything) should eliminate the battery drain until you can get around to re-configuring the rest of the wiring to work with the ammeter.