73 Dart Alternator doesn't show charge anymore.

SputnikOne said
Touching alternator output lug to the engine block for ground while it's not running gives me 12.45 volts, which is alittle confusing

Key off.
Measuring voltage from any of the main feeds should show battery voltage.

Everything connected to the battery is hot. The wire from the alternator output terminal, the wire to the ignition switch, two or three of the fuses, etc.

SputnikOne said
Yeah, I think the alternator is outputting 12.45 ish volts, which is pretty low, but it would explain why the battery isn't quite dead yet. Got 12.45 volts when touching output to ground from the alternator, and revving the engine seems to make the ammeter move *the tiniest* amount towards charging.

Engine running.
Measuring voltage at the alternator output eliminates the possibility that the output wire is disconnected.

Now the question is why?
Since you have a voltmeter, with the key in run, check to see if power is making its way to the field wires. @67Dart273 has suggested a procedure for doing this. Then he has suggested a method of checking the alternator and regulator.

I will only add that 12.45 is pretty low for a battery. I'll again suggest putting the battery on a slow charge. The reason is because a low battery will pull a lot of current when given power at 14 to 15 Volts. Even when the wiring gets cleaned and fixed properly, 20 to 40 amps over a fairly short time (5 to 15 minutes) can cause damage. Also recharging at those rates can deteriorate the battery (cook it).