check the voltage at the VHF.
1. Battery and circuit you’re testing ON (flip
the appropriate breaker on the DC panel).
2. All other circuits OFF.
3. Turn the DVOM selector to DC volts.
4. At the VHF, touch your red lead to the
positive terminal, black lead to the negative.
Compare the result to your voltage at the
power source. A drop greater than 0.4 V (the
ABYC deems a VHF radio a critical circuit) or
1. 2 V in any circuit should send you scurry-
ing to clean terminals and check for ample
wire gauges. If the voltage reads zero, you’ve
got continuity issues.
A typical electrical fault is “an unwanted
open” — an undesigned break in the circuit
— that interrupts the flow of electricity. That
can come from something as simple as a
blown fuse or something more complicated
like a broken or extremely corroded conductor, or a loose or separated connection.
Continuity describes a circuit that is closed,
as it’s designed to be. To find out if you have
a break in the circuit:
1. Turn the DVOM selector switch to
2. Check the DVOM battery. With the
leads separated, you should see “OL” for
“overloaded” or no continuity. Now touch
the leads together, and you should hear a
beep for continuity or a value near “0” on
the meter. If you don’t get these, replace the
3. Turn off the circuit to be tested.
4. Disconnect the two ends of the circuit
component you suspect is bad (say, the wire
leading to VHF from the distribution panel).
If your DVOM leads can’t reach, add a length
of properly sized wire to complete the circuit.
5. Connect your probes to each end of the
A beep or a meter reading near zero indicates continuity. “OL” indicates overload:
no continuity. No continuity means there’s
a break in the wire. You can also check for
blown fuses and tripped circuit breakers with
this test by touching each end with your
probes (breaker must be on and disconnected
from power). It’s also possible the device itself
has burnt up, breaking the circuit. If the continuity is high, but not OL, go back and look
for a loose or corroded connection, or jiggle
the breaker or switch if they’re part of the portion of the circuit you’re testing. When these
go bad, they sometimes work when pressure
is applied, but not when it’s released.
If the problem you’re having isn’t getting
devices to turn on but rather keeping them
on, you might be drawing too much current
(amps) through a given circuit. Fitting older
boats with new, power-hungry devices can
exceed the capacity of the original circuits. If
you don’t have good documentation on how
many amps a given device draws, here’s how
to find out. Use a pair of meter leads that terminate in insulated alligator clips. You’ll need
to disconnect the power lead somewhere in
the circuit; the meter itself will complete the
circuit. A good place to insert the meter leads
is at the circuit protection (fuse block). If
there’s a fuse, remove it.
1. Switch OFF the circuit you’re testing.
2. Set your DVOM’s selector switch to DC
amps, at the proper scale.
3. Disconnect a wire where you’ll measure;
CURRENT TEST USING
alternatively, remove a fuse from its holder.
4. Clip the black lead to the terminal closest
to the battery, the red lead to the other.
5. Switch on the circuit, being careful not to
let your body parts complete the circuit.
The meter will give you a reading in amps
to record. If the total amp draw on a circuit
exceeds its protection rating, the breaker will
pop. Measure all the devices on a given circuit
to find out if it’s overloaded.
AN AMP CLAMP
Some newer multimeters come with a feature
called an “amp clamp” that lets you measure
current without disconnecting the circuit. But
there are still a couple of tricks. First, when
Many boats have alternating
current (AC) systems installed;
these are supplied by shore
power or an onboard gener-
ator or inverter. Operating
at 120 volts or more, these
AC systems can be lethal
if you allow your body
to complete the circuit.
Before starting, be cer-
tain that the system
you’re measuring is
DC, not AC.