I knew it would be a mess ... I had a lot of trouble trying to isolate some tach trouble when I got the boat. No telling, yet, where that speaker wire is connected on each end. There were cut wires just hanging out. Mixes and matches of heat shrink tubing, electrical tape, liquid electrical tape, and crimp-on butt connectors. There are wires labeled "common ground" with terminals on the end, but not connected to anything, just limp.
The smoldering fire at the end of last season I assumed was connected to my ignition switch because when I cut the key to shut off the motor, the motor just kept running. Key removed completely, still going. I had to remove the fuel line to shut her down. You can see in the photos one of the wires heated up along its whole length and melted off it's own insulation, and some of the neighboring insulation, and some of the damn split loom, too.