It wouldn't short a switch. Does it blow a fuse if all the switches are off? Any 12V outlets in that area which might have something plugged in? One of those 12V outlets with USB charger? LPCO detector? Smoke detector (they're usually 9v battery operated, though)?
Are there multiple wires going into the terminal block on the converter for that fuse? If so, disconnect them all, a new fuse shouldn't blow (or the converter board got screwed up). Then connect them one at a time to see which one(s) cause(s) the fuse to blow (if you had a meter, a supply of fresh fuses wouldn't be necessary).