I'm not familiar with the Aerostar but I can see the wiring diagram in the Repair Info section at the Autozone website. The diagrams aren't always fully accurate, but this is what they're showing as the charging system for the '93 - if the first link doesn't work then try the second:
Link 1
Link 2
If the diagram is accurate then there are three fusible links associated with the alternator.
You'll see that one runs from the battery to the alternator's 'B+' output terminal. With the engine and ignition switched OFF, check for 12V at the B+ terminal - it should be present at all times. If 12V is missing then the fusible link is open-circuit.
Another fusible link runs from the battery to the 'A' terminal - this feeds the alternator's field coils, and if it's missing then the alternator cannot produce any output. Again, that should be present at all times so check for 12V with the engine and ignition switched off, and again if 12V is missing then the fusible link is open-circuit.
The third fusible link runs from the ignition switch to the 'I' terminal, and this carries the signal to switch the alternator on, so if 12V is missing then the alternator won't be able to produce any output. However, that link also carries current to the starter solenoid, so if the starter cranks then the fusible link must be good, so no need to check it. The current which signals the alternator to switch on also flows via the ignition switch and then to the charge warning lamp on the dashboard - if the lamp illuminates when you switch the ignition on then that section of the ignition switch must also be good, and current must be reaching the alternator, so no further checks needed there either.
A fault in the starter circuit won't affect the charging system, but I do notice that the last fusible link which I mentioned, for the 'I' terminal, connects to the starter relay, so a bad connection there could result in no charging but if the charge warning lamp indicates then the connection should be ok.
Fusible links are just short sections of wire of a smaller gauge than the wires which they protect, spliced into that main wire. The short section of fusible link will be protected by special non-flammable insulation, and if it blows then it will overheat and you would expect to see heat damage in the form of blistering on that insulation.
The alternator's B+ output terminal is usually a large stud, with the wire secured by a nut, and it will be separate from the other alternator wires, which usually connect via plug and socket. I'm hoping the colours indicated on the wiring diagram will be accurate and you'll be able to identify the A and I terminals by the colours. Either a multimeter on its DC voltage range or a 12V test lamp will be fine for checking for the presence of 12V. Let me know if you don't follow any of that.