It really is a simple thing, working with dc current. Your boat should have a panel where you turn on the navigation
lights as well as other things on the boat. This panel should have fuses or circuit breakers that look like light switches, depending upon your boat's age. Most probably, they are pushbutton breakers or fuse. Anyway, one side of the switch or fuse will have a wire that goes to a main breaker or fuse. The other side should have a screw connection with a wire going to what ever appliance or light that the switch / fuse operates. Select an available breaker / fuse that you will keep turned on all the time. If you don't have an empty one, select one that will be ok if you keep it on all the time. Don't select navigation
lights because you only want to turn them on at night. Put the positive (red) lead from the depth sounder there. The black lead should go to a negative bus bar. This is a block with lots of screws and wires attached. Find an available spot and crimp on an appropriately sized connector and attach it to the bus bar. That, is all there is to it.
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