Could reversing the red and white wires connected to the alternator cause a battery drain when the car is not in use, but still run and charge? Note: I'm using an alternate location for the voltage sensing wire, and I am using an "idiot light" and the existing amp meter in my '46 chevy. I completely rewired the car, and I've narrowed down the drain to the charging circuit.

Yes, reversing those two would in fact drain your battery. The sense wire on the alternator can be "hot" all of the time, but the "light" terminal must be keyed.
Jason
Advanced Electrical Rebuilders
www.aerrebuild.com