Batteries won't charge on house power

My uncle has a 98 vanguard rv and it doesn't seem to power the house batteries while plugged in. When it's plugged into 120v everything in the rv works perfect but I'm only measuring 1 v at the battery leads. When the rv is running I'm getting 13.6v at the leads and I think that's the only time the battery's are charging. I don't think it's the convertor since while plugged in everything 12v works but I could be wrong. I haven't been able to find a wire diagram anywhere online that's been any help. I'm wondering if from the fuse box it should send 12 v right to the house batteries to charge or if it's something in between the batteries and fuse box that is malfunctioning but I can't seem to see anything where the fuse box is. Any help would be greatly appreciated.
Thanks

Hi Chrisb18,

Sorry your uncle is having a problem, but as this forum is for Heartland owners, I'm not sure how much help we'll be on a 98 Vanguard RV. But maybe someone here has had one in the past and will have an idea.