I have no idea how lefty got that to work, I tried pulling one of my HDSI transducers from the boat last winter and the cable was so stiff I could hardly bend it. When warm they are pliable enough to hang pretty level, in the winter i have a feeling there would be no chance of it hanging level. The humminbird cables are much better suited for hanging a skimmer transducer for ice fishing.
Fuse on the positive power wire? Yeah you should be using it. Probably don't need it if you are careful and don't short it or hook the cables up reverse polarity.