This can happen as wiring get loose from vibration or
corrosion. Undo each terminal or
plug (including any fuse holders) and inspect for telltale
corrosion, clean with sandpaper/wire brush etc, spray with
electrical contact cleaner (or even WD40). The terminals and plugs you will need to examine are in a few places: under flybridge console, behind the chart table console, under the
mast post in the
salon (access panel behind seat back), the breaker circuits in lower electrical cabinet and maybe the
cables that connect some
raymarine gear in the upper electrical cabinet.
IF you have left
salon windows open, rain or sea spray can puddle and drip down on the electrical cables underneath the woodwork, if so this needs drying out.
If you have a multimeter you can check voltages at the console to see if it corresponds to voltages on the electrical panel. With engines/generator running this should be 12.5V or more. An alternative to check if it is the instrument cluster itself is to run (through a fuse or breaker) a direct pair of wires from the
battery to the
power cable. If this works then you probably have a cable join issue.
Try direct positive first and then direct negative to see if it is a positive of negative connector, then direct for both.
An exercise in patience and persistence!