HOW THIS WORKS (the voltage drop problem) Bad connections in the ignition harness are the root cause of voltage drop, and current flow caused by the normal operation of the alternator field/ VR and ignition system is what effects the actual drop.
The battery is getting charged and the VR is supposed to SENSE the voltage "same as" being right at the battery. But if there is a VOLTAGE DROP between the battery POS and the VR, then the VR will say to itself "hey the battery is low we must charge it." Let's say when you perform the drop test (one probe on the battery POS, other probe at ballast power terminal) you read, say, 1.8V. That means that the VR sensing terminal is sensing 1.8V LOWER than the battery
So the VR "sense" terminal "wants" to keep that terminal at 14V (13.8--14.2). If the terminal is 1.8 LOWER than the battery, that means the battery will OVERCHARGE by the amount of the drop. So if the VR is correctly maintaining 14V at the "sense" terminal, and you add the 1.8V drop, the battery will be running at 14V + 1.8 = 15.8V!!!!