The brown wire is in the exciter circuit of the alternator. W/o gauges, the brown wire (Ckt 25) runs to the charge lamp in the instrument cluster. With gauges, it runs to the hot side of the CHOKE fuse in the fuse block where it connects to circuit 300 off of the ignition switch. With gauges only, the brown wire run between the firewall bulkhead connector and the alternator regulator plug is a special type of resistance wire that limits current flow through the exciter circuit.
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