If theres no load in the circuit it WILL blow the fuse. It causes a huge amperage to be drawn through the wire when theres nothing to slow it down and use the electricity, aka the part thats not working. If there is a short to ground in between the battery and the fuse, it will melt the wire or something else until there is no more contact to ground. Obviously, after the fuse, electrons are finding a SHORTcut back to the battery before they get to the load component.