Installing electric tongue jack

Hi,

I have a question about what might (did) go wrong if I make a mistake wiring my new Ultra 3502/3500 Electric Tongue Jack.

It bolted in quick, no problem. I disconnected from shore power. I took out the fuse that was already connected to one of my 6v batteries, connected the line DIRECTLY to the battery (probably my big mistake), turned on the jack and... now I have no battery power. I reconnected to shore power and the lights, fridge, fan - all of it works. But when I unplug from shore to run the two 6V I get nada. I know that the batteries were fully functional because I tested them before starting.

Did I fry something expensive? Can this be fixed?

Thanks,

Jason
2007 2720
TV 2006 Quest Minivan