Charging system problem

[mr.precision]

Went to start my stock 1967 stepside.
Connected the battery, turned on the ignition, and noticed smoke under the hood. Disconnected the battery and found the main red 12v wire that goes from the battery across the top of the radiator to the main harness had grounded and melted.
Also noticed the ammeter was pegged to the right and remained so.
Replaced all the wires from the battery, lights, and ammeter fuse back to the main harness in front of the firewall.
Started the truck and observed the voltage across the battery at 16.-17 volts.
Figured the regulator got fried, so replaced that.
Battery voltage before start: 15.6 volts. Battery voltage now when running: 15.4 volts.
Swapped out the alternator and got the same results. I have 12.5 volts to the regulator and alternator. All instruments in the cab work just fine, with the exception of the ammeter which is still pegged to the right and does not move.
I figure the windings on the ammeter got cooked, but cannot understand if that would affect the charge rate. I even put the old regulator back in and sure enough.... 16.5-17 volts again with the engine running.
No rodents in the garage.... sealed up like a boat. Most of the wiring is new.
Any thoughts on where to look? I am out of ideas.
Thanks