That makes sense, thanks.I'm guessing that you have contaminant on the board behind the LCD display. It's been awhile but I recall that LCD module is soldered in direct to the board -- I can verify this is needed but I'll have to go in the attic, clear my bench etc. will do it if u need me to.
What is likely happening is your hydroscopic contaminant is becoming conductive when it's humid out or it rains. U may even have a lower windscreen leak that's dripping water onto that area.
Del s suggestion is where I would start. Be careful to not bust off the tangs that hold the inst panel together. Take it out, carefully disassemble ( there's about 15 screws but all visible) and see what's going on.