Don't work yourself into confusion. Think about what is common. If the headlights work, you are getting battery power through the bulkhead, through the ammeter, and into the passenger compartment. If anything works in the key "accessory" position, the key switch is at least "receiving" power from the ammeter circuit/ bulkhead.
Does anything work with key "in run"? Gauges? warning lights on the cluster? If so, power is at least getting that far. Next see if power is making it out through the bulkhead to the ballast resistor. That wire splits and feeds the blue wire going to the alternator field (There are two, green and blue)
