[Tiara Open] battery isolator

[waycamp]

can anyone explain the how the battery isolators on a 2900 open work?.    Under the stairway I have two isolators, assume one for each engine.  They all seem to be cabled together.    The alternator on the starboard side isnt outputing a charge,per the analog gauge. I  Had the altenator tested and it is good,   When both engines are running it  seems at least one alternator is chargng both battery banks.   can one of the isolators go bad?   if this sounds confusing it is because I am confused.  Any help would be appreciated