My tongue jack only works when connected to shore power or when fully hooked up to truck. I thought the battery might be the problem but had it tested - tested good. Any ideas of where to look?
Check the battery connections on the battery.. Make sure you hit them with a wire brush and re-connect.
Happened to me one time when I was leaving a site. Didn't mess with it at the time and plugging into the truck solved it, but when I got home, trouble shooted it a bit more and after cleaning the connections on the battery, it was all good again..