Over Voltage with New Battery Disconnect Switch

The "popular" voltage drop problem WITH FACTORY wiring can be anywhere in the circuit path from the battery PLUS to the VR terminal

In a stock car, this includes the following terminal points and components:

Battery to FUSE LINK, through the RED BULKHEAD CONNECTOR terminal, to the AMMETER and through the AMMETER, out the ammeter on BLACK to the under dash WELDED SPLICE, and branch off to feed the IGNITION SWITCH CONNECTOR, through the SWITCH, back out the SWITCH CONNECTOR on "ignition run" blue, back out the BULKHEAD CONNECTOR on blue, and BRANCH OFF to feed various circuits, ignition, choke heater, smog doo dads, and the VR IGNITION TERMINAL in the CONNECTOR

Every single thing in bold type is subject to a problem, including bad connections within the factory ammeter wire ends, or the ammeter itself.