There was a good article in a german classic magazine.
The most time there are not real sensor problems. The most time there is a problem in the wires. As you write your problem starts when it rains. That's the point.
I think you must have look for two points: are the conectors okay? Change them against wterproofed ones (the Harley "deutsch connectors are great) and: look if there are earthing points that shows rust. Not only the wellknown mainpoints, most are the smaller points the problem.
Good luck.
René
