HWH Jacks won't go down

I took my daughter on a nature walk while I pondered motorhome ownership. When I returned, the power to the panel lights up. Strange thing is that when I open one of the T-handles and try to extend the jacks, the power to the control panel dies. There must be an internal breaker, because I can turn the power off and back on and everything comes back on. If I try to extend the jacks without the T-handle open, the pump will run but nothing happens at the jacks. The HWH manual says that if I have 3500 psi at the manifold, then it's the shuttle valve. I have no way to check to see if I have pressure, but since the slide operates, seems like their should be pressure there. Either way, I think I'm getting it narrowed down.

Tom