The positive side of the battery circuit was beefed up but what about the negative side? Have you checked and cleaned battery-chassis and chassis-engine grounds?

A charging problem I ran into on mine was poor grounding of the regulator to the alternator case. Cleaned the corrosion and a dab of conductive grease with no further issues in about 3 years.

I would think that with good clean connections, there shouldn't be any problem with a properly operating alternater keeping up with the original system load, without modifications.

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Sam

84 300SD 350K+ miles ( Blue Belle )