Potential ignition issues
When your car was running, power should have been coming from the alternator.
The ammeter should have been indicating battery neither charging or discharging.
For starting, power comes from the battery.
Turning the key to start, current should flow through the ammeter to the ignition switch.
The ammeter should show slight discharge. Does it?
If not, and you know power is making it to the key switch (previous test), then there is a break in the starter relay circuit and possibly also the ignition start (J3).