If your ammeter was non-functional, it would affect many systems in the car, including making where you had no power to the ignition. A jump start wouldn't solve the problem, either.
For a 73 with the ZX alternator swap, you have to be careful that you don't have the electric fuel pump modification in your car. That modification added some wiring that includes providing power for the fuel pump relay coil. Leaving this wiring modification in place after swapping in the ZX alternator will cause the relay coil to be energized all of the time. That will run down your battery.
Keep in mind that if your electrical system is good, you won't see the ammeter move hardly ever.
The ammeter was moving with the turn signals before probably because the voltage at idle was low. The voltage dip from the lights lighting up meant that the battery had to prop up the electrical system momentarily. The ammeter measures the flow between the battery and the alternator. All but a couple of electrical components are wired to the alternator side of the ammeter. (I believe the brake lights and hazard lights are two exceptions. They will light up with a blown ammeter.)