Battery fried and more

I'm sure it's a charging system problem as opposed to a battery problem

ARE you SURE your voltmeter is ACCURATE? I just ran into a cheap digi multimeter a friend "down the alley" has which is WAY off

Check your meter on your line voltage. It varies, but should be around 117--125V AC Measure a few flashlight batteries. Measure another one of your cars. With engine warm and battery "normalized" voltage should run right at 13.8--14.2

In fact, what, exactly and how, exactly, are you measuring this voltage? You no longer have a working ammeter, I assume? What modifications have been done to the wiring?

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Common problems:

1....Voltage regulator not grounded. VR MUST MUST be grounded. This means a SOLID ground path between battery neg. terminal and the VR mounting flange.

With engine running, warm, and (you hope) battery normal, make this test first with all accessories off, and again with heater, lights, etc on

Clip one probe of your meter to battery NEG terminal. Stab the other probe into the regulator mounting flange. Make sure to stab through paint, chrome, rust. With the meter set to read low DC volts, you hope for a very low reading, zero is perfect. Anything over .3V (three tenths of one volt) is too much, and it SHOULD be lower.

If any QUESTION, remove and clean the regulator flange, scrape around the bolt holes on the firewall, and re-mount using star lock washers. You can also add a jumper ground wire from the block to the firewall. On a V8 there are unused holes on the back of the driver side head. Look at the front of the pass. side head!!
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2....Voltage drop in the electrical harness. This is the supply voltage to the regulator which is also SENSING voltage. On a "stock" harness, the circuit path is...........

Battery.........starter relay stud.........fuse link........through the bulkhead.......through ammeter..........to ignition switch connector.......through the switch........back out the switch connector.........back out the bulkhead connector.........to underhood loads. This is "ignition run", the switched 12V which supplies ignition, regulator, etc

To check this, turn key on to "run" but engine off. Clip one lead of your meter to battery positive, the starter relay stud. Hook the other probe to either the blue alternator field wire, or to the "key" side of the ballast.

You are again looking for a very low voltage. Over .3V means you have problems. This voltage, whatever it reads, is ADDED to the regulator voltage.
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3.....Check CAREFULLY the VR connector, which is related to 2 above. Inspect the pins and connector for corrosion, and work it in/out several times to scrub it clean, and to "feel" for tightness.
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4..... A bad / defective VR.

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5.....Very rare but can / does happen, is some wiring fault which causes the field terminal of the regulator hooked to the green wire going to the VR to ground. This could be a bare wire in the harness, but more common is a BROKEN or damaged brush holder at the alternator. Pull it apart and inspect, or if you can "catch" it when overcharging, shut off the engine, and check for continuity...............

With the two field wires pulled off the alternator, there should be continuity between the two field connections. NEITHER field connection should show continuity to ground.