Messed up charging system Options

[andreic]

Please help! I am running out of ideas on what to do to fix my charging system in my 1972 1.7L.

Two weeks ago it refused to start. Got it started a couple of times by pushing.

Took it to a NAPA store, had them test the battery, they said it was bad. Took it to an Interstate Battery store, they tested the battery good, but said the charging voltage was low (around 12.8-12.9). Got it back home, measured the voltage at the battery, it was 13.4. Tried replacing the voltage regulator with a known good one, same exact results.

Then I thought maybe my battery was indeed bad. Couple of days ago bought a brand new Optima, and put it in today. Measured the voltage at the battery with engine running to 2000rpm, got 13.8, thought all was good.

Went for a drive around. One strange thing I noticed, there was a sound like a relay clicking on and off, on and off, like a blinker, but with a slower frequency. Went on like that for at least 10 minutes while driving. Sound was coming from under the panel, left side, where the fuses are. Thought that maybe this had something to do with the charging, but when I stopped after half an hour at a gas station, voltage measured 13.8, even with the headlights on, and the clicking had stopped. Thought I am out of the woods.

Got home, checked again the voltage, 12.2-12.3 no matter what the engine RPM. So basically not charging at all. No more clicking.

The red light in the panel comes on when the engine is not working but the key is on. Otherwise the light is off, even when the alternator is clearly not charging.

Any suggestions on what to test? What should the resistances be between the three electrodes in the plug for the voltage regulator? I suspect something is messed up with that wiring, but can't figure out what. (The system worked fine until two weeks ago, and moreover the car has not been cannibalized in any way.) Or could it be a fuse that is making a bad contact?

Thanks!