there is no marking for “+” or “-“ on the ammeter. Does the “-“ charge correspond to the Discharge post on the ammeter? With that, we should get things right.
I believe that is correct.
A portion of the '47 wiring diagram showing only 4 wires connected to the ammeter is shown below. COLORS ARE MINE IN THE DRAWING AND DO NOT REPRESENT ACTUAL WIRE COLORS.
Red is power from the battery via the stomp starter switch connecting to ammeter + side.
Also connected to the ammeter + side is the horn wire marked in blue.
The ammeter - side purple feeds the light switch.
Also connected to the ammeter - side is the "everything else" wire.
"Your mileage may vary" in the 77 years since the truck was new.