I have bought a Furuno combo 1971, looking now at the wiring.

The installation manual says, red wire to power, black wire to earth and shield to hull of the boat.

I presume this shield is the inner silver paper like material surrounding all the other wires, excluding the black and red wire, inside the cable.

Does this sound reasonable? There was no such connection on the removed sounder. What ramifications are there if this shield is not connected?

Thanks if you can help.