Where ever the voltage dropped when current was run through it. Ignoring whatever variations there are in the readings, there was a .5 Volt drop between the relay and the whereever you read it on the bulkhead, and another .3 Volt drop to the ammeter. Since that wire is warm its more suspect.
Then there's a 1 Volt drop between the Ammeter and the run wire connection at the bulkhead.
The .4 Volt drop to the alternator's stud makes no sense unless there's a short inside. If there was a short inside, it should have shown up in the measurements with the ignition off.
View attachment 1715165836
