This is one of the 2 plugs you need to wire the 3G alt. into the bronco it is the wire off to the side that energizes the stator.
15-00520 Alternator Pulley, Serpentine for Early Bronco
62-25001 Battery mounting kit. for Early Ford Bronco
81-13030 Alternator harness 3G non EFI for Early Bronco
81-13042 Alternator harness 4G EFI for Early Ford Bronco