A multimeter is an indispensable tool that can easily sniff out electrical problems on a boat, once you learn a few techniques. The first of these is called a continuity test. It’s a simple go/no-go test to see if a wire, light, fuse, device or circuit will conduct electricity. For example, if the navigation light doesn’t work, a continuity test will tell you very quickly whether it’s the bulb, the socket or the wiring. Here’s how to do it.