1968 Dart gauge help

If you're in time crunch, connect the two ring terminals together and bypass the ammeter.

If the car has a working cigarette lighter, there are voltmeters that can be stuck in there.
@toolmanmike

A voltmeter will not show quite the same thing but is still plenty useful.
If it shows 13.5 to 14.5 Volts with the engine running, that's normal and you can generally assume the battery is getting charged.
If it shows 12.5 Volts or less, you know the alternator is not producing power and the battery is probably discharging.

One more thing while I'm thinking of it.
Before the final hook up the battery to the repaired system, put a test lamp in line.
If it lights up, there's still a short from battery positive to ground.
That way you will know without burning out another fusible link.