Unfortunately, those units have a circut board at the power source and if there is no fuse you more than likely destroyed that board. Take the casing apart (the part attached to the boat) it should be two halves. That inital board you see is probably what is destroyed. Of course before i did that I would look for an inline fuse near where the cables attach to the battery or under the unit in the nose of the boat. There is nearly always a fuse if it came from the factory or dealership with the unit so i'd play a little extra hide and go seek for that before doing anything else.

Best of Luck