Need Alternator help

[Jim.ME]

Depending on the type of alternator, that excite wire shouldn't need to remain on after the 12V has been applied to that terminal. Once energized, the field should remain powered without external excitation. If you leave the switch up all the time, it will likely overheat. You need a diode in that circuit so it doesn't backfeed. Or, just turn the switch off after the engine starts. Check your charge voltage, 12.7 or greater at idle, and 13.2 approx at 1500.

I didn't have a diode handy so I wired mine with a momentary contact button. I start the engine, push the button, the field excites and stays energized. That way, when I shut the tractor off, the field will collapse and I don't have to remember to turn the toggle switch off.

Sounds like you have a Delco type alternator. It was established he has a Denso alternator, not a Delco type. The Denso lamp circuit is a separate terminal/circuit, so the IG terminal needs power all the time. No diode, lamp or resistor in the wire from the switch to the IG terminal of this alternator.