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.
 Always perform a continuity test with no current present. So kill the battery switch, unplug the device or shut the breaker.
 Turn the dial on the multimeter to the ohms setting. That’s the one with the omega symbol that resembles an upside-down U.
 Touch the meter’s probes together to make sure it’s working. If it is, you will hear a beeping tone and/or the meter needle will read zero.
 Touch one probe to the positive side of the device or appliance and the other probe to the ground side. In our example, pull the bulb and place one probe on one contact, and the other probe on the other contact. (If it’s a single-contact bulb, the ground is the threaded base of the bulb.) If the bulb is good, the meter will tell you by beeping and reading zero. If the circuit is broken, you will get no beep and it will read infinity.
If the bulb checks out, move to the socket, the wire, the fuse and the circuit breaker until you find the link in the chain that’s bad. Knowing how to perform a test for continuity ends the many return trips to the marine store, as a harried boater simply replaces parts willy-nilly until the problem is resolved.
Catch Corrosion Before It Catches You
While your boat is out of the water, a great use for the resistance function of the multimeter is to check out the integrity of the bonding circuits and the sacrificial anodes. These protect underwater metal fittings from corrosion. For instance, if a through-hull has current running through it, it’s better to find out now than after it crumbles to dust and sinks your boat after launching for the season.
Set the meter to the ohms function and place the probes on any two pieces of equipment connected to your boat’s bonding system (the green wire). If the reading is less than 1 ohm, all is well. Continue through the bilge, checking each leg of the bonding circuit. Next, place the probes on a zinc and the metal it’s intended to protect. A reading of 1 ohm or less means it’s OK.
More Multimeter Tips
-When selecting a multimeter for boat work, a model with an audible continuity alert is best, as often you are working in a tight area where seeing the display is impossible, but hearing a beep or buzz is easy.
-Also, know that you can extend the length of the probes with simple jumper wires fitted with alligator clips.