Man you have a direct short. You might as well start at the tanks and inspect the sending wire. There is a naked spot somewhere, and I'll bet on the chassis. As soon as you can find it either wrap it with tape or cut it and put in a coupler, then try a new proper size fuse. A fuse is a safty device, it lets you know that there is a problem. Adding a larger fuse is a hazzard and can cause more problems.