There is only one source of switched power under the hood, and that is the ignition "run" line which hooks to the ballast resistor, coming out of the bulkhead. That line (depending on year) branches off and feeds the ballast, the VR "IGN" terminal, the blue alternator field, the choke, and smog doo dads some years.
THAT LINE CAN SUFFER voltage drop because of the terminals in the circuit path, as well as right in the ignition switch contacts. THAT voltage crop can cause OVER charging (over voltage).
