I am not familiar with your coach specifically, but just to clarify.....you say the battery voltage (coach batteries I assume) are reading 13.5 volts......which implies that they are currently being charged via the converter (converter powered either by shore AC or via gen AC) ....since normal unloaded battery voltage should be around 12.6 volts when fully charged. When you say the 12 volt bus is dead do you mean there are no DC lights nor any DC coach battery power (12v fans etc) in the coach? If the coach battery use/store relay has failed open then you should typically also not be able to charge the coach batteries either (no 13.5+ volts at the batteries).
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