Also, it seem like the PO bypassed the factory wiring harness and wired the alternator to the battery using what looks like 10 gauge wire... I would expect it to be at least 4 gauge..

Another thing is that my volt meter reads from the instrument cluster so there's quite some distance from the battery.

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1982 240D 4-speed
2013 Jeep Wrangler Sport - 4.10 e-locker