Squareback alternator testing armature
Sorry, a megger is designed to find high resistance shorts---at high voltages. .
Go to MyMopar and download a service manual, latest one is 73. There's a procedure in there to measure amp draw of a rotor. There should be specification in section 8 somewhere listing rotor current draw
Pay attention to the battery voltage you apply. Do you understand anything about ohms law? At low resistances and voltages, "a little bit" of change, either voltage or resistance, can have a large effect on amperage.
I don't recall anymore, seems to me I'd expect around 4A with maybe 6A maximum