Well it's pretty obvious that you have a short somewhere in the wiring for the wipers. I'd reccommend grabbing a wiring diagram and starting to trace the wires...you should probably start at the wiper motor, as the end out in the elements is more likely to sustain damage.
AND under NO circumstances do you EVER put a bigger fuse in than it came with. If you want to catch your fuckin car on fire then be my guest, but otherwise i wouldn't do it. Fuses are a certain size for a reason. if it pops at 20A, something is definitely wrong...putting a 30A fuse in there will only increase the likelyhood of damaging components and or burning your car to the ground.
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