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I would connect a volt meter between positive battery cable and the battery to see if there is a draw then disconnect alternator and see if draw goes away.
These alts have been known to do this
There are 6 diodes in most alts. only takes one to short out and do this
If not the alt, then its time to pull fuses till you find the circuit making the high draw
I had a skidsteer alternator that would draw down the battery when it was not running. Probably the same general principle applies the auto alternators and batteries
i find the easiest way to tell a bad diode in the alternator is to feel it after the engine cools off. if the alternator is warm, or hot, there is a bad diode in it causing the parasitic draw.