Humidity and all kinds of moisture from sweat and condensation in a case can cause all kinds of problems with your instrument. Humidity can cause oxidation on switches, potentiometers, jacks and rust hardware. Constant moisture on an instrument will cause ICPC (inner coil pole corrosion) where the magnet can rust inside the bobbin due to exposure to humidity and moisture. When a magnet rusts or oxidizes, there is a break down of the magnet wire insulation and exposes to bare copper magnet wire. After a period of time the bare magnet wire can oxidize and breaks eliminating a signal from the pickup. Try to keep your instrument dry and avoid hot trunks in your auto that can cause condensation in the case due to the high moisture content in the lining of your case.