On my 85, I replaced alt, belts, battery, a couple of voltage regulators and was still getting wierd output readings.

Issue one: glow plug relay was malfunctioning.

Issue two: wire that excites the alternator field was almost completely broken at the connector on the alternator - almost.

Issue three: The two big wires from the alternator were rubbing on the chassis to the point that the wires were exposed. I guess after 28 years, the plastic cover of the wiring harness AND the insulation around the wires themselves just wore out.

I fixed all of the problems and no more wierd alternator readings. I include this only to get you thinking about other possible scenarios that cause electrical issues.

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