If a shield is part of a transmission
line which depends upon the characteristic impedance to be uniform between source and load then it must be connected as per a schematic at both ends.
When a shield is present as an attempt to reduce susceptiblility of the wires encased to interference
or in an attempt to reduce radiation from the wires encased then termination of the shield at both ends of the cable will be effective only if all the electrical
characteristics are predetermined between the shield and each wire enclosed. This you cannot reliably do at the power source end of your wires. You should not make a shield connection to the battery
negative at the battery
end or power distribution end in order to prevent either power currents or noise
currents from passing through the shield. If you make a shield connection to the negative at each end you cannot guarantee this.
So, with a Furuno
supplied power cable having a connector at the chart plotter end that, when connected, has continuity between the shield and the negative wire made internally to the chart plotter circuit board do not make a shield to negative connection at the other end of that wire.