Also check your electrical connections and grounds. Not just the connections themselves, but the integrity of the connectors onto the wires.
Wires (and plumbing) don't support themselves. Vibration and shock can loosen and/or fatigue dangling unsupported wires.
Wires that are pulled tight will strain a connection. There should be sufficient slack, not pulled tight and tuned like a piano wire. The hull will flex the most in rough water.
I would go through and tug on every single wire, with a force of about 10 pounds of pull, to make sure there is good mechanical connection.
Lastly, wire nuts have no place in marine or automotive applications.