No crank, no lights, no horn, nothing

I have an E350 van with a gasoline engine. For a long time the van seemed not to start in the morning when humidity was very high. We live in Florida. This problem would go away in the heat of the afternoon. In the morning it would crank and not start but I had lots of fuel at the schrader valve on the fuel line, etc. Today, however, went to start and it’s dead; like the battery’s disconnected. No horn, no lights. I fiddled with the ignition, wires under the hood, switches, knobs. Lights will come on but as soon as I rotate the ignition everything turns off. I put the key in and the warning buzzer comes on, then I pull the headlight switch and everything turns off.