Battery to battery post on starter relay. Fuse link on the same post to firewall bulkhead. Inside firewall bulkhead to ammeter. Ammeter to a multi wire junction in the harness.

Fuse link or ammeter. Also, confirm the bulkhead connection is not burnt up on both sides of the firewall.

Ammeters fail. Old bulkhead connectors get hot and melt. Fusible link would need a short somewhere to make it burn.

Check the battery wire on the back of the alternator. It is on the harness side of the ammeter.

Down and dirty fix for the ammeter is take one of the wires off and move it to the other stud so they are connected and not running the current through the meter.