charging system blues

Those are all good suggestions, but I'd switch the order of checks a little.
Based on the description, I'd start by measuring the voltage at the alternator output (the stud with the heavy wire) while the engine is running. Compare with the battery positive voltage.

Here's why I'm suggesting this.
Engine off, the battery normally should be 12.5 volts or a little higher.
Engine running, you see the ammeter indicating current flowing to the battery.
This is normal, and with most alternators, increasing rpm will increase current.
So the only thing possibly odd is that the battery voltage didn't come up at least a little bit.
Usually while its charging, the voltage on the positive terminal floats up close to the alternators voltage. That's why I suggest checking the alternator output voltage. If its also low (and doesn't come up rpm ) then its worth checking whether its the voltage regulator or the alternator at fault. (see above posts for that)

However if the alternator output voltage is normal (somewhere around 14 volts), and the battery positive is 12volts, then check the voltage at each exposed connection. Could be high resistance from a poor connection or damaged wire. If the wire is only 12 volts at the starter relay, then check the firewall connections.

It would not hurt to fully charge the battery on a slow charger. Then recheck the voltage again (engine not running) and then at both the alternator and the battery with the engine running.