I bought a new to me 2013 Legend and it has Lowrance electronics with structure scan box and linked to 2 hds units. I tried to learn to use them but decided to go with what i know and put some Birds on boat. When i started taking off the Hds units that was fine but the structure box has a cable marked transducer. Is this a seperate transducer from the side scan. i know i had 2 transducers on my birds one in hull and the SI on outside.