Gauges freak out.
 

Has anyone had this problem?... I have a '05 MC, 55,000 mi. Whenever it rains or I wash the car, the gauges and trouble lights freak out. The temp. gauge pegs out then drops to nothing; the tach jumps all over the place; the runflat light,check engine light,DSC light, all come on and off. It seems to do this mostly while at idle then go back to normal when I take off. I'm thinking that water is getting into a connection in the wiring harness somewhere, but don't know where. The car runs fine. Takes about a day to get back to normal. Any thoughts?