you need to have tech check the inverter for AC leakage in the DC charger output
bad filter capacitors in the charger section or a failing SCR
but you also have a wiring problem, because the alternator should NOT be connected to battery system when on shore power
there is the possibility of a bi-directional charge system, to maintain chassis batteries when on 120vac power
depending on the system this would expose the alternator output connections to any leaky AC voltage from the inverter charge section
but i suspect the problem with the alternators is something else,
like poor ground bonding of the shore power circuit
I can explain it to you.
But I Can Not understand it for you !
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1997 F53 Bounder 36s