That's a bigger problem than a ground somewhere. Sounds like you got a hot wire crossed somewhere. You shouldn't have to have a higher amp fuse in there. Check the routing to where that wire comes from, it's not a constant 12v lead. Do you have the old fan wires crossed or touching? Try unplugging the old fan fuse if you don't have it hooked up to anything and see what that does. The fan fuse is on a relay block I believe and the wire may be crossed there, just a suggestion.