agreed or a short to ground on your harness rubbing against something its not supposed to be and when it gets wet it completes the circuit check your engine bay harness also you could always simulate the scenario by wetting the the car and looking for sparks or checking for melted harness also if you have a dmm or dmov multi meter you can check you battery and alt and then do a peracidic draw test to se if its dawing amps when wet and if it is when dry/wet key on/off