65amp wiring/trouble shooting
If the battery was getting 20 amps at 18 volts, that was the result of a problem in the branch feeding the key switch, not the branch going to the battery. Any damage at, in, or near the ammeter would be due to the long period of overcharging.
If the studs to the ammeter are loose - then it must be repaired. Those are a press fit to the metal plate connecting them together.
If the only damage is at the wire ring terminal, then fix that. A little De-oxit on the metal. For the insulation, some liquid electrical tape, and a wrap or two of tape keeping that boot/seal shut where it split. It's going to be very difficult to do a quality job replicating that factory ring terminal connection to the 8 gage wire.
At one point you measured 18 Volts at the battery, and at least 10 amps or more going to the battery.
18 Volts at the battery can not be caused by poor or loose connection in the ammeter.
It got to 18 Volts because of a fault in the charging system (grounded brush or green wire, regulator itself) or in the circuit wiring from the alternator after it branches.
To understand that take your finger and follow the path from the alternator output to the regulator input (blue wire).
We know the alternator was producing power at least 18 Volt. IF the regulator was seeing low voltage then the resistance had to be along the path to the regulator, not the path to the battery.
If the battery was getting 20 amps at 18 volts, that was the result of a problem in the branch feeding the key switch, not the branch going to the battery. Any damage at, in, or near the ammeter would be due to the long period of overcharging.
If the studs to the ammeter are loose - then it must be repaired. Those are a press fit to the metal plate connecting them together.
If the only damage is at the wire ring terminal, then fix that. A little De-oxit on the metal. For the insulation, some liquid electrical tape, and a wrap or two of tape keeping that boot/seal shut where it split. It's going to be very difficult to do a quality job replicating that factory ring terminal connection to the 8 gage wire.
At one point you measured 18 Volts at the battery, and at least 10 amps or more going to the battery.
18 Volts at the battery can not be caused by poor or loose connection in the ammeter.
It got to 18 Volts because of a fault in the charging system (grounded brush or green wire, regulator itself) or in the circuit wiring from the alternator after it branches.
To understand that take your finger and follow the path from the alternator output to the regulator input (blue wire).
We know the alternator was producing power at least 18 Volt. IF the regulator was seeing low voltage then the resistance had to be along the path to the regulator, not the path to the battery.