I noticed the under dash fuse box on one of my cars was wet, probably from condensation forming on the inside of the windshield and then dripping down on to it. I pulled out all the fuses and cleaned their tips which were pretty crusty. Just to be certain they are OK, I also ohm'd them. Found five that showed open even though visually they looked fine. If i had put them back I could have been chasing faults that didn't exist except for a bad fuse. I'm guess water may have entered the fuse and frozen, expanding them internally.