No Power to anything
OP sound like you are on right track. Could ALSO BE the wire end terminals themselves. Certainly ammeter sounds suspect. If you have not done so read this article. It gives a great simplified diagram and overview of this type problem
Catalog
This diagram is simplified but follows the functional path of the main power distribution is same for most these girls
Main problem areas are fuse link, bulkhead connector, ammeter, back out the bulkhead connector to the alternator
In rare cases the welded splice opens up, VERY rare but does/ has happened. This is a welded splice a few inches away from the ammeter, in the black wire, up under the dash