These are NMEA2000 instruments (Simnet), so I don't know what "the system has collapsed" could possibly mean. It doesn't make any technical sense.
I also don't know how you saw the fineness of the wires, since the connection cable wires and connectors should all be integral. Even if it is wired with terminal connectors, 18g wire is normal size for this application.
Like mentioned, this sounds like a connection issue. If your connections are not integral cables
, you should check them for continuity and corrosion
on the connection points. If they are integral cables
, look for one that is pinched or has a nick in it.
You also could have a faulty transducer putting enough errors on the network to disrupt the others. You should either get software
to analyze the network, or get a technician on board with a network analyzer. Alternately, your chartplotter or instruments may have basic network monitoring functionality that would show bus errors. If you see bus errors, start disconnecting transducers one at a time until they disappear.
BTW, new standard NMEA2000 instruments are compatible with your old ones. The only difference is the connectors - your Simnet connector vs. the standardized micro-C connector. You can intermix the two easily using Simnet-MicroC cables.