i have a ford e250 van. it is running fine. I park, come to turn it on and nothing. no start, no lights, no horn

If you let it sit long enough does it start up again? I had this problem with a Ford Taurus that turned out to be the ECU that was intermittently working but would randomly just quit. It eventually stopped fixing itself and we had to replace it. The other thing it could be is a bad ground connection on the battery, which is easier to check than the ECU - Disconnect and clean both battery terminals, put them back on the battery, then disconnect the other end of the negative, clean it and the surface where it attaches, and put it back on. Make sure the cable is good and try to start your van. I hope this helps.

NOTE: Some of the factory security systems will lock you out if your battery completely dies or you disconnect the power. You can google to see if this is a possibility for your truck and how to avoid this problem.