big volts

You are going to HAVE to get / buy/ make some wiring diagrams that you can understand. I've posted this before but the general "idea" on the big current side of the alternator is right there at Mad Electrical

Divide the problem up

It makes no sense to take readings if you don't explain exactly where you take them so the guys on this site can see and visualize what you are doing and under what conditions, IE warm, running, running fast enough to charge, with /without lights or other loads

Generally, the troubles.

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.........high voltage.......

If the high voltage is only at the alternator output, but low at the battery, this, generally, is going to be in the "high current" or output side of things. This includes the terminal on the wire right there at the alternator, the terminals feeding INTO the interior through the bulkhead, the AMMETER terminals, the WELDED SPLICE (see mad electrical and your diagrams) and the current coming back OUT through the bulkhead and feeding the battery via the starter relay stud.

The DIFFERENCE in voltage between battery and alternator STUD when running and charging, can be probably as much as 1/2 volt when running "hard," depending on condition of the various terminals

It it is substantially more than 1/2 volt, you probably have a bad connection in the "path" from alternator output to the battery. This includes the bulkhead terminal large red and large black wires, and the ammeter, and under--dash welded splice. Refer to the Mad Electrical site

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SHORT causing "full field" output. This occurs some on 70 and later vehicles with "dual field" that is correctly "isolated field," when the GREEN field connection becomes GROUNDED. This is the field wire leading off to the regulator, and in 70 and later, the green sort of controls "the amount of ground" on the field. The field in 70 is FED power from the ignition switch (blue.) So if that green circuit gets grounded it will charge full output and high voltage

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POOR GROUND on the regulator. This is not simply "tightly bolted." This means the entire pathway, through the regulator flange, bolts, to the body, the jumper ground (where ever it is) to the engine block and back to the battery. The VR MUST be grounded at the same voltage (potential) as the battery.

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BAD REGULATOR. Rare, does happen sometimes I assume you've already tried a different one

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VOLTAGE DROP in the ignition circuit. I've preached and preached. If there are poor connections in the "feed" to the VR ignition terminal, IT WILL charge "over voltage."

The "path" on factory wired cars is

from battery....to starter relay....through bulkhead on red ammeter wire----to ammeter---to welded splice under the dash------to ignition switch connector--------through switch--------back out switch on IGN 1 wire-------back out bulkhead on IGN1 wire---------and to feed off to underhood ignition loads, including

ignition system

alternator field (blue) on 70 and later

regulator IGN terminal

smog stuff on some cars, and electric choke if used
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The above is the "ROAD MAP" I've so often preached. Wiring is exactly like driving down the road. Some of the road is wide (big wire) some of it has potholes at poorly marked intersections (splices and terminals) and some of it branches off on unmarked roads (circuits you are unaware of and confused by)

So just like "going somewhere" you need this road map, and you must go DOWN that map one mile at a time

I've posted numerous stuff on this, do a search.