Originally Posted by ChasA
I would start by removing the cables from the batteries and cleaning all the contact surfaces. Remove the negative lead that goes to the chassis frame first and put it back last.
I agree. I'll add this. There are two, ultra big battery cables that go directly from the house batteries to the Inverter/Charger. The positive cable does go through a very large fuse, on its way to the lug, on the front side of the Inverter/Charger. Do make sure that, all positive cables, connection points and any related connections in the house battery/Inverter/Charger system, are thoroughly clean and tight.
And, while the house batteries MAY read 13+ volts, that doesn't mean that there isn't a problem with one or more of the cells in one of the batteries. A good practice here might be to make sure that they, all the house batteries, are fully charged and then, get them "load tested" to make sure that one of them has not developed a bad cell.
One more thing, Winne and Itasca I think, both use a frame welded bracket, for the attachment of both the house and chassis batteries, right behind the battery compartment. That bracket, can get seriously rusted and corroded and, along with it, all the negative cable ends. Just something to check on.
Let us know what you find out will you? Take care and good luck in finding your remedy for this issue.