Ammeter swings wildly, weird alternator wiring

That's been hacked. It looks like it may have been hacked to so as to run the field from the main circuit rather than from the run circuit. That would cause a battery drain. Just guessing based on the photo.

The connection at the output stud looks like it may be damaged.
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A poor connection there could cause the battery to take over running the car.

Electric pumps and fans are almost always problems. if its wired to the battery side of the ammeter then the ammeter needle pointing to charge is indicating eith or both charging and fuel pump draw.