I'm getting 15 volts at battery and the regulator.
Gauge is only off a couple tenths. I checked with a voltmeter. Running 14.9-15.1 everywhere.
So, then you’re guessing the voltage drop is around .2 of a volt? Really need to measure it if you want to accurately isolate an elevated charging voltage condition. Again, place one lead at the regulator Batt. terminal (terminal, not the connector/plug) and the other at the pos battery terminal. If it measures .2 of a volt, that would be fairly low for a fifty year-old electrical system, with a good battery, that would leave the regulator as the only issue.
Not to be alarmed! When you first start the car there is a draw on the battery that needs to be replenished thus the higher output. Mine does the same thing but after a bit of constant driving, drops to about 14.2. This occurrence can vary depending on weather your using an AGM style of battery or Lead-acid. The real issue here is weather or not the alternator/VR can maintain a decent output with all the power "hogging" circuits activated.
No, I'm getting the same reading at VR and battery: 15 volts.
You asked specifically how to diagnose an overvoltage condition. Voltage drop at the bat terminal on the regulator is the first thing to be checked. It needs to be measured as previously mentioned. There is no-way your 50-yearold original wiring has 0 voltage drop through the bulkhead connector twice, wiring, ignition switch and it’s connections. If you are not going to measure it then your only option is to throwing regulators at it in hopes of finding one calibrated at a lower voltage or open one up (voiding any warranty) and make the mechanical adjustment mentioned.
