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A Guide to Simple
Boat Electrical Diagnosis
and
Maintenance
Prepared by Gordon Agnew
for the
Members of CYC
© Gordon Agnew
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Table of Contents
1. Equipment Required
1.1. Digital Multimeters
1.2. Soldering Irons
1.3. Crimp Connectors and Crimping Tools
1.4. Electrical Contact Cleaner
1.5. Electrical Tape, Heat Shrink Tubing and Heat Guns
2. Using a Digital Multimeter for Diagnosing Common Electrical Problems
2.1. VHF radio or Chart Plotter Will Not Work
2.2. Checking Rigging Lights Before Putting up Mast
2.3. Trouble Shooting Battery Problems
3. Making/Repairing Electrical Connections
3.1. Soldering Techniques
3.2. Tinning
3.3. Joining Two Wires
4. Installing New Circuits
Note: Many of the images used in this booklet were obtained from the Internet. These
images are being used for educational purposes only.
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1. Equipment
The follow are items that should be kept on your boat for electrical problem diagnosis.
• A digital multimeter
• a pair of either red/green or red/black alligator wires
• a small soldering iron and electrical solder (not plumbing solder)
• a combination wire stripper and connector crimper
• a selection of crimp connectors
• electrical tape
• electrical contact cleaner (optional)
• heat shrink tubing of various diameters (optional)
• heat gun (optional)
1.1 Digital Multimeters/Alligator Wires
Digital Multimeters (also called Digital Voltmeters - DVM) are able to measure a number
of things, the important ones for a boat are:
• Direct Current (DC) Voltage, (indicated by a symbol with a solid line over a
dashed line) - your boat's 12 Volt power is DC
• Alternating Current (AC) Voltage, (indicated by the symbol V~) - this is used for
measuring the presence of Shore power or the output of inverters
• Continuity and Resistance - this is used check such things as fuses and bulbs
• DC Current - this is used to measure how much current (in Amps) that a device or
circuit is using
The alligator wires allow you to connect the leads of the multimeter to the wires/device
being tested leaving your hands free.
1.2 Soldering Irons
A soldering iron is used to make good electrical connections. Good connections are very
important in a marine environment. A 25 Watt (25W) "pencil" style soldering iron is a
good choice. Also make sure you get electrical solder not plumbing solder!
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1.3 Crimp Connectors and Crimping Tools
Crimp connectors come in a variety of types and sizes. The image below (taken from
Google) shows the various forms.
The most popular are:
•
•
•
push-on connectors used to terminate a wire which will be to a male terminal
found on some 12V breaker panels. It can also be paired with a male tab to allow
convenient disconnection of devices such as instruments on the mast. Use only
insulated Female push-on connectors.
Male/Female bullet connectors can be used for the same purpose. These
connectors are suitable for connections that will not be submerged in water.
For instruments or wires carrying power with two (2) wires where connecting
them the wrong way could cause damage, do the following: on one set of wires,
use a Male and a Female connector. Reverse this on the other wires. In this way,
you cannot reverse the connections. If the connections are carrying power,
always put the Female push-on connector on the positive wire that comes from
the power source. In this way, if the connector is disconnected, it cannot short out
against another connection or grounded metal (such as the mast).
Fork and Ring connectors are used to terminate wires that will be connected to
screw down connections such as those found on many 12V breaker panels. Ring
connectors, even though they require more work to put on a terminal, are
preferable as they cannot slip off of the terminal.
Butt connectors are used to "permanently" join two pieces of wire.
When using a crimp connector in a marine environment, I strongly recommend that the
wires be "tinned" before being put into the connector and crimped. The reason for this is
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as follows: typical household wire has bare copper strands. In a marine environment, the
copper will corrode and can cause the connection to fail. Tinning the exposed wire (this
will be covered in the section on use of the soldering iron) prevents this and ensures a
very good connection that will not corrode.
Some people insist that you should only used tinned "marine" wire on a boat. In this
wire, the individual strands of wire are tinned over the length of the entire wire. This
wire is much more expensive and I do not feel it is necessary in most of the simple
applications you will encounter. If you do use it, still use your soldering iron to tin the
ends before putting them in a connector.
Choosing the right size of crimp connectors is very important! The size of wire is
traditional measured by its gauge. The smaller the number, the thicker the wire. Most
applications on a boat will use the following range of wire gauges.
Corresponding crimp connectors are colour coded as follows:
•
•
•
RED = 16 to 22 gauge wire (thin wires)
BLUE = 14 to 16 gauge wire
YELLOW = 10 to 12 gauge wire
If you are running a new circuit on your boat, be sure to check the charts supplied
in Section 4 to determine the proper gauge of wire to use.
Tools for crimping connectors come in various sizes and qualities. Most also have a
section that allows you to strip the wire then crimp it.
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Note: This crimping tool has a section for insulated and non-insulated connectors always use the correct section!
1.4 Electrical Contact Cleaner
I recommend that connectors or contacts on instruments be cleaned before reconnection.
Over time and exposure to the elements (such as winter storage of masts), connections
can corrode and will not operate properly when reconnected. Spray both sides of the
connection before reconnecting. Be sure to read the label! Some of these cleaners
should not be inhaled!
Connectors should be relatively bright (almost shiny) in appearance. If they are dull or
dark, a small file of a bit of sandpaper can be used to clean them up a bit - be careful not
to overdo it and remove the outer tinning of the connector.
1.5 Electrical Tape, Heat Shrink Tubing and Heat Guns
When using crimp connectors in a marine environment that may be exposed moisture,
make sure you seal the crimped end. This can be done carefully wrapping the insulation
on the crimp connector and a short distance down the wire with electrical tape. On Butt
connectors, make sure you start on the wire of one side of the connector, wrap over the
connector and onto the wire on the other side. This should be done in one continuous
wrap.
A better seal can be achieved using "self annealing" tape as it creates a watertight seal.
"Liquid" tape can also be used... it works well but can be a bit messy!
Yet another method is to use heat shrink tubing and a heat gun. There are two basic types
of shrink tubing - single layer and dual layer. With single layer, you have to make sure
you use the appropriate size so that it forms a good seal over the wire/connector. Dual
layer shrink tubing has an out layer (basically the same as single layer) and an inner layer
that incorporates a sealing adhesive that melts and fills in any gaps. This is a more
expensive solution but produces the best seal.
Tapes and tubing come in various colours. I recommend that you use Red material on the
positive side of any connection.
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2. Using a Digital Multimeter for Diagnosing Common Electrical Problems
A digital multimeter (DVM) is one of the most valuable instruments to have on a boat for
trouble shooting. I will go over a few scenarios that you might encounter. In many
cases, the procedure will be similar.
2.1 VHF radio or Chart Plotter Will Not Work
My usual procedure is to start at the device and trouble shoot back to the breaker panel.
Almost every electronic device has an "in-line" fuse on the positive side of the power
connector. They usually look like the ones pictured below
Step 1: Do a visual inspection of the wires running to the device for breakage, etc..
Check the breaker to see if there is power from the batteries (there is usually a voltmeter
or indicator lights to show that battery power is available - this can also be done by
checking other devices such as lights, etc..).
If there is a splice in the power wires or a crimp connector, try gently pulling on the wires
to see if they are still making contact. Many problems can be found this way.
Step 2: Open the fuse holder and remove the fuse. Do a visible inspection of the fuse to
see if it blown or not. Next, set your DVM to Ohms (symbol Ω) or continuity (some
multimeters will buzz if there is continuity). Short the two leads of the DVM - it should
either buzz or the display will read a value near zero (0). This is to make sure the DVM
is working properly. Next, touch the DVM leads to each end of the fuse - if it buzzes or
reads 0, the fuse is good.
Step 3: Change the DVM to DC Volts (not AC Volts). You will have to find a good
ground wire to connect the BLACK lead of the DVM to (this is where the alligator wires
comes in handy). With the fuse holder open, touch the RED lead of the DVM to the
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exposed connection heading to the breaker panel. If the DVM display reads a value near
12V, then there is power to that point. If you can put the fuse back in with the holder
open, check both ends of the fuse - there should be the same reading.
If there is power there, but not the device, the problem may be with the connector that
actually attaches to the device (most VHF radios, chart plotters, etc., have connectors). I
have run into cases where these connectors have corroded over time and need to be
cleaned. Pull of the connectors and inspect both sides. This is where the Electric Contact
Cleaner is handy. Following the directions on the cleaner, spray both sides. Sometimes
rubbing the connections with a bit of clean cloth or paper towel will help with this. Put
the connector back on and check for operation.
Step 4: If the fuse is good but there is no Voltage reading on the DVM it is time to move
backwards towards the breaker panel. The problem could be with the positive or ground
connection - a break in either can be the cause. If you can find a separate ground wire try
moving the DVM Black lead to another ground - if you now get voltage, it is a ground
problem. Visually inspect the wires leading back to the breaker panel. Any splices in the
wires along the way should be inspected and checked to see if there is voltage on both
sides of the connector or splice (you will probably have to remove tape, etc. to get to the
wires. Replace any bad splices you encounter.
Step 5: Check the breaker. Disconnect shore power to your boat. You may want to
temporarily disconnect your batteries (main switches) while you open up the breaker
panel. Most connections are made to breakers using push-on crimp connectors or
ring/spade connectors as mentioned in Section 1. Do a visual inspection to see if a wire
has become loose or fallen off. Do this for both the connection to the breaker and to the
ground (which is usually a strip of connectors). If you see any discolouration or
blackening at either connection, it is generally an indication of a loose connection
(vibration and age commonly result in loosening of push on connectors). Tighten or
replace if you observe this. Use your alligator wires to connect the DVM to one of the
ground connectors (Black lead) on the panel and the connection on the breaker that your
device power wire is connected. Turn the breaker on and make sure that no wires are
shorting out (i.e., no metal objects such as screw drivers etc., are in the breaker panel.
Turn the battery switches back on and see if there is power coming out of breaker. If
there is no power, you have a bad breaker (yes, the eventually go bad with moisture). If
there is power indicated - you have missed something along the way.
Step 6: If you can safely leave the Black lead connected directly to the breaker panel
check for power at the device fuse again. If there is now power indicated, you have a bad
ground connection or wire. If there is no power, at the device, use the Red alligator wire
to connect to be breaker terminal and check for power by tracing the ground wire
connections back to the device.
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2.2 Checking Rigging Lights Before Putting up Mast
It is a good idea to check your mast lights before putting the mast up. This can be done
in a few ways.
One of the simplest ways is to use a small 12V battery (such as portable power devices).
Identify the positive and negative wires at the base of the mast. Some systems have a
common ground wire then a separate +12V wire for each light (steaming, work lights,
etc.). Other wirings might run a separate pair of wires for each light. You can determine
which you have by the number of wires.
Start by using the Electrical Connection Cleaner to clean the connectors at the base of the
mask and on the boat. If possible, open up all lights, remove the bulbs from their sockets
and also clean the connects in the socket and the base of the bulb. Check the connections
to the base of the light fixture - if there are broken strands of wire or corrosion, clean
and/or replace as necessary. Check to see that the filaments of the bulbs appear intact.
While you are at it, clean the connectors for any instruments as well. Don't forget the
connector for the VHF antenna - a corroded connection here will significantly reduce the
range and clarity of your radio.
Leave the light enclosure open if you can. Use the alligator wires to connect the Red and
Black terminals of your porta-power to the light leads - be sure to connect the Red and
Black leads to the correct polarity. If you use LED lights, they will not work if you
switch +12 and ground.
Test each light in sequence. If it works try the next one. If all of the lights work, reinstall
the light covers and repeat the test. If one does not work know, you have a problem in
the housing.
If a light does not illuminate or appears dull, try re-cleaning the bulb connections. Set the
DVM to DC volts. Put one lead on each side of the bulb if possible or the socket
connections. If there is power, check the bulb. This can be done using the OHM setting
and connect a lead of the DVM to each connection on the bulb. It should create a
relatively low reading on the display - if not, try another buld.
If there is no power at the light fixture terminals, you may have a broken wire or
connection in the mast.
Testing lights can also be done without a portable 12V source. Set the DVM on OHMS
to your meter's lowest resistance level and measure the resistance on each pair of lighting
wires at the base of the mast. If the light is good and has a connection a relatively low
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reading, 10 - 25 ohms should occur. A reading of zero (0) indicates that you have a short
somewhere in the wiring - try removing the bulb and measure the resistance again - if the
reading is very high the short may be in the bulb or socket. If the reading is still zero,
there is a short in the wiring.
If the reading is very high - the bulb may be blown out. Remove the bulb and test it by
visual inspect or using the DVM.
2.3 Trouble Shooting Battery Problems
Your DVM can be a valuable tool if you are having problems with your batteries or
charging system.
The following chart gives the DC Voltage that should be displayed at various states of
charge for Lead-Acid batteries. These values are for batteries that are not being charged
and are not running any devices.
Problem 1 - batteries are not holding charge or don't seem to be charging. If you have
more than one battery on your boat measure each one separately. Try charging the
battery(ies) for several hours. Disconnect the charger and any devices drawing power
(refrigeration, etc.) let the system sit for about 1 hour or so. Measure each battery and
note the voltage. Note: to do this, you must be able to separate each battery - If you have
a battery isolation switch, set it to "OFF" and measure each battery. If you have a parallel
battery bank, you will have to disconnect the battery terminals to do the test. If after
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charging, one or more of the batteries are not showing the proper voltage as indicated in
the graph, one or more battery may need replacing.
If you suspect a problem with your charging problem, disconnect the batteries and
measure their voltages. Turn on the charger (from shore power) and measure the voltage
on the batteries - it should be higher than the voltage measured when not charging.
The same test can be done to test the boat's alternator system. Check the voltage of the
batteries with the engine not running. Start the engine and set to a fast idle speed. The
voltage should be higher than with the engine not running (typically in the range of 14.2 14.5 Volts).
3. Making/Repairing Electrical Connections
As mentioned in Section 1, crimp connectors are a good way to terminate the ends of
wires for connection to breakers, etc.. Connections must be mechanically strong and
electrically strong.
The best way to prepare a wire for a crimp connector is to strip back enough insulation so
that the length of the exposed wire is equal to the depth of the crimp sleeve on the
connector. Tinning the end of the wire is a very good idea before crimping the
connection. When crimping, make sure you use enough force to cause a good
mechanical connection between the wire and connector. Try gently pulling on the wire to
make sure there is not movement of the wire within the sleeve of the crimp connector.
If you want an even stronger joint and you are using un-insulated crimp connectors, you
can solder the wire into the sleeve of the connector. This generally takes a larger type of
soldering iron which has much higher power.
3.1 Soldering Techniques
To create a proper solder joint takes practice and time.
3.2 Tinning
1. Plug in the soldering iron and let it heat up. Make sure you use the stand supplied
and it is on a non-flammable surface or one that will be damaged by the high heat.
2. Unroll a bit of solder (a few inches). To determine if the iron is warm enough, touch
the end of the unrolled portion to the tip of the iron - it should melt quickly. Have a
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small wet sponge or damp cotton cloth at your soldering station. Gently wipe the tip
to clean it - the tip should look glossy silver with very little solder on it.
3. Twist the stands of the exposed wire so that they are in a tight, uniform bundle with
not stray strands sticking out. Arrange the exposed strands of the stripped wire so
that they are physically stable and not touch any surface. Do not try to hold the wire
in your fingers, it will get far too hot! Use a clamp or have some hold the wire near
the area you are going to tin with pliers.
4. Make sure the tip of the iron is clean, apply a small bit of solder to the tip of the iron.
Apply the tip of the iron to about the middle of the exposed wire. The small amount
solder on the tip of the iron will assure good conduction of the heat. Let the wire
warm up a bit then start applying solder to the place where the iron tip is touching the
wire. The solder should start melting and will be wicked up into the wire. Apply
enough solder so that the entire exposed wire has a shiny silver colour, there is no
copper showing and the solder is uniformly distributed over the exposed wire. If
there are blobs or drips of solder, you have applied a bit too much - quickly clean the
tip of the iron on the sponge and use the iron to reheat the wire and remove excess
solder. Now let the wire cool before continuing.
Also, be careful not to get the wire too hot by holding the iron to it too long - you will
start to burn/melt the insulation.
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3.3 Joining Two Wires
You can use a Butt crimp connector to going two sections of wire. Tin each wire then
trim the tinned end until it fits far enough inside the crimp sleeve to touch the end but still
ensure that there are no parts of the wire's tinned conductor exposed.
It is best at this point to wrap the connector with tape.
If you do not want to use a connector, you can join two wires in a smooth inline fashion.
Strip each wire to expose about 1" of conductor, hold the exposed ends facing each other
with about 1/2 of each overlapping. Wrap them around each other as tightly as possible
(this works better on thinner wires). Then solder the two in a manner similar to tinning.
For thinner wire, tinning each end first before wrapping produces a better connection.
Wrap the connection with tape or heat shrink tubing to complete the connection.
Marr connectors, the types shown below, have no place on a boat except if there are no
alternative for an emergency repair. In a marine environment subject to moisture and
vibrations, the wires will corrode and the connection will fail.
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If you must use them, it is best to tin the ends of the two wires to be joined. Hold the two
wires together so that the tinned ends are at the same length. Using a pair of pliers, twist
the wires together in a clock-wise direction when viewed from the wires' ends only - this
forms a good mechanical connection between the wires. You can put the Marr connector
on the joined wires turning the connector in the same clock-wise direction. Keep turning
the connector until it is very snug. A better method is to tin each wire, twist the wires
together as described above then solder them together - then apply the connector which
now just acts as an insulator over a good mechanical and electrical connection. Be sure
to apply tape starting from midway down the connector and continuing onto the wires
themselves.
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4. Installing New Circuits
Sometimes you will have to run a new circuit to install a new device. There are a few
things you will need to know before starting.
1. How much DC (12V) power will the device draw? This is measure in Watts
(power) or might be specified in Amps (current). You need to know the
maximum current draw of the device. If you know the power in Watts, divide the
power in Watts by 12 and that will give you the current in amps. The voltage at
the device will drop from the voltage at the breaker. The longer the length of the
wire, the higher the drop. It is recommended that this drop not exceed 3% or
0.36V otherwise some devices will not work properly.
2. How will you route the wire around your boat? You need to know the length of
the wire that will be used from the breaker panel to the device.
3. Is there room for a new breaker in the panel? It is best to put any device that
draws a significant amount of power on a separate breaker (for example,
refrigeration - devices that have very heavy power requirements such as a
windless require special treatment). Devices such as radios, chartplotters, etc., do
not require a lot of power and can be placed on an existing breaker as long as the
total current requirements of all of the devices on that breaker does not exceed the
rating of the breaker.
4. What type and size of connectors do you need for the ends of the wires?
The following charts should be used to determine the gauge of wire you should use.
Note: You must double the length of the run of wire that you will use from breaker to device as
you have to count the ground and +12V lengths separately.
American Wire Gauge (AWG)
Current (amps)
Length
(feet)
5
10
15
20
25
30
40
50
60
70
15
16
12
10
10
8
8
6
6
4
4
20
14
12
10
8
8
6
6
4
4
4
25
14
10
8
8
6
6
4
4
2
2
30
12
10
8
6
6
4
4
2
2
2
40
12
8
6
6
4
4
2
2
1
1/0
50
10
8
6
4
4
2
2
1
1/0
1/0
60
10
6
6
4
2
2
1
1/0
2/0
2/0
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American Wire Gauge (AWG)
Current (amps)
Length
(feet)
5
10
15
20
25
30
40
50
60
70
70
10
6
4
2
2
2
1/0
2/0
2/0
3/0
80
8
6
4
2
2
1
1/0
2/0
3/0
3/0
90
8
4
4
2
1
1/0
2/0
3/0
3/0
4/0
(from www.EngineeringToolBox.com)
for lower power applications
American Wire Gauge (AWG)
Current (amps)
Length
(feet)
0.25
0.33
0.50
0.75
1.0
1.5
2.0
2.5
3.0
4.0
15
22
22
22
20
20
18
16
16
14
14
20
22
22
20
20
18
18
16
14
14
12
25
22
22
20
18
18
16
14
14
12
12
30
22
22
20
18
18
16
14
12
12
10
40
22
20
18
16
16
14
12
12
10
10
50
20
20
18
16
16
14
12
10
10
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A word of caution - never connect a circuit directly to the batteries. There should always
be a properly sized breaker or fuse in the circuit with the device. There should also be a
way, such as a battery switch, to disconnect the battery from the boat - if a short circuit
occurs, a fire could result.