‘75 Dart Sport Charging system issue(s)

Some quick checks. With the engine running on fast idle, measure voltage at alternator stud. If it is near same as battery, and down below 13+V it is not charging

If it is 'way high' 15-16V and the battery is still low, then you have a break in the charging path from alternator to battery. I believe (you will have to look) that those cars have a big white connector that separates the engine harness from the firewall. Those connectors are flaky. Otherwise, the bulkhead connector or ammetr are suspect

If the alternator is low, try this

With key in "run" but engine stopped, "backprobe" the alternator field terminal with the blue wire. If you need better access switch them around. You should have nearly same as battery at the blue. If you do, remove the green and jumper that alternator terminal to ground. Start engine, bring up RPM see if ammeter shows charge or voltmeter increases. Don't allow it much above 15-16V

If it comes up to that, move on. If not, check brushes, etc, and troubleshoot alternator or replace

If alternator charged in test above, now reconnect field wire(s) and disconnect VR connector. Look at connector with a light for corrosion, work in on/ off the VR several times to scrub connection. Make CERTAIN VR is grounded.

"Rig" a way to jumper across the two VR terminals in the harness connector. Again see if it will charge. If so, replace VR