Alternator wiring harness
An alternator can run on two wires, the thick wire is the supply to charge the battery, direct to positive, via fuse box or starter supply. The thin wire possibly blue on Fords, is the energiser wire from the dash charge light, without this connected the alternator will not charge. If on the new pigtail two wires are thick (30amp) you can ignore one, some vehicles double up on the charge supply wire.
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