No power to the jack- electric jack not working

[Goosecreeklarry]

Cant get the power jack to work on what used to to be our trailmanor. They were able to get it work went they picked it up from our place by popping the trailer back up and plugging into shore power. They are getting ready to take itoutontheir first camping trip and they just tried to do the same thing and now the jack doesn't work at all. They traced the wire from the battery to the jack and it isn't working, they traced wires from the battery to underneath the trailer and they work. It worked fine for us when we came back from our last trip with our truck. They have a Cadillac SUV ish type of vehicle. Any idea of what is wrong and why we can't get the jack to work? We are completely stumped and feel bad we can't help them due to our lack of experience.