BA440-78PU

I have an 04 1500 it has the 4 wheel drive shift switch instead of the shift leaver on the floor.When it rains it shifts into 4 high on its own.I've always been able to get it out and back into 2 wheel drive until the other day it rained and it did it again but this time I can't get it out.Has anyone else had this problem and does anyone have any suggestions on what could be causing this problem.

TVLynn

Check the wiring to the trans, clean the connections and coat with dielectric grease