Overcharging

You got some good advice from '67 dart'. He forgot to add in post #2 that a large black wire is also connected at the welded splice. This wire goes thru the bulkhead connector and goes to the alternator output. The terminal connectors in the bulkhead are barely adequate for the amount of current the big red and black connectors have to carry. And adding to that, the old 35 Amp alternator might/likely have been replaced with a more powerful one over the years. Problem city.

Matt's second diagram shows the separate 2 wire harness for the hi-output alternators. Straight thru the bulkhead with no connectors. My memory thinks a round 5/8" dia. hole was drilled thru the firewall, a grommet sealed out the water, and the red and black terminals on the ammeter would fit thru the hole. Note that these 2 wires are always hot!!!!