Stop in for a cup of coffee

Mattax said
pretty sure its wired something like this.
Might be a mix up at the bulkhead if not right at the ammeter.
Get it straight and it should be good to go.
View attachment 1715450483

If I'm right, the fix could be as easy as moving the wire from the main splice to the other ammeter stud.
The loose wire could be spliced in,

or given a ring terminal if its long enough.