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Confirm that you do have voltage to the alternator thin wire/s with the engine off and key on run.
Actually, here is the wiring diagram.
The yellow/white big cable at B+ should have 12 volts with key off.
The orange/light blue, at terminal A, same as above.
The light green/red at terminal I should be hot with the key on run/engine off.
If all is ok, with a voltmeter check the charging voltage right there at the back of the alternator at the B+ terminal, while the engine is reved up to at least 1,500 rpm. It should be at least 14 volts. If it is, check the voltage again while reved up a that 175 amp fuse, and then again at the connection to the starter. Wherever it looses that voltage would be the spot where the cable is most likely bad and might be rusted/corroded and need to be replaced.
Ok, then you have basically 2 options. 1 is waiting until the problem happens again and performing the tests I mentioned or 2 just assuming that it is a loose connection and re-tightening each connection.
I would do the seconds first, re-tightening each connection and then if it happens again be prepared to perform the tests.