Headlights on my 2004 Ford Freestar keep turning on and off

I have never had a problem with my freestar until we moved from Idaho to Oregon and then after it rained one day the lights started going on and off so we looked on line and found out about the PCM and had it fixed for the water problem. Well it had not rained over the summer and have not had problems with this except after my husband washes the van. but today we have not washed the van but the lights are going on and off again what would make this happen