BAD (REMAN) ALTERNATOR? OVERCHARGING

The VERY first thing you need to do, and THIS IS a common problem with rebuilts:

Disconnect both field wires, take your ohmeter set on low resistance, and measure from the alternator case to either of the two field connectors on the alternator. They should both be OPEN, AKA "infinity." Usually the problem is that one brush is INCORRECTLY grounded, either A: wrong or missing parts in one brush holder, or B: Rebuilder PURposely grounded one to "turn it into" a single wire field for 69/ earlier cars