No start after rain

I have a 1994 Aerostar with 108,000 miles. Automatic transmission. 3. Liter V6 engine.

The Aerostar will not start after it rains or after a damp fog. It does not get wet inside or under the hood. None of the cylinders appear to be firing. It takes several hours with the hood up before it will start after rain has stopped.
The Aerostar does not have a distributor but is electronic and has individuual coils at each spark plug. I have already tried replacing the controller which is mounted on the fenderwell with no results. I have also checked all of the wiring for the fuel injection and ignition system and cannot find any moisture or faults.