I don't believe it is an open circuit, just because it doesn't happen all the time. My guess is that the moisture is causing a short circuit. It's just the where and why.

 

The only reason I say open circuit is I had a 03 Ram 1500 and a wire rubbed on something and caused it to be exposed. It didn't hurt anything unless there was moisture in the air. My advice is see what you are missing when it is wet. Then you'll get a start to where to look.