How to fault find on small boat electrics

Discovering my nav lights weren't working, I had to find the fault and execute a fix without the benefit of circuit diagrams, or any labels on the switch panel or distribution board. Here's how I did it. 00:00 Describing the fault 00:38 No label hellscape 01:30 Testing the negative wiring continuity 02:13 Continuity testing on a dead circuit 03:30 Confirming continuity