Same exact problem with my 04 Santy. Started the day after I bought it. I ripped the whole back hatch apart, messed with all the wiring, replaced all the fuses, nothing worked. In the end I just pulled the fuse for the rear wiper and left it dead. It's annoying but it's an old used car. I don't know what the gremlin is but every year she gets a few more electric quirks.