A few things come to mind. My neighbor had a light go out over his dinette, and put a new bulb in. And as soon as switch was turned on fuse would blow. Come to find out the fixture had a double "base" bulb, one hot & other ground. He had put a single base bulb in, base hot and side of socket ground, not realizing the kind of bulb he took out. So he ended up with a direct short.
Also if you have a problem you can take out fuse and connect a test light to each fuse contact, and light will come on if it is a direct short. Start to disconnect wires, say starting at switch. When test light goes out, you found wire that has short.