102 Electrical Systems Trouble Shooting

Understanding Your Boats Electrical System

So, you are here because either you are a curious person...or...some part of that %*!!#*#@&*!!! electrical system is acting up.
Even on a simple sailboat the electrical systems can be daunting.  Never fear, we have written this course to hold your hand and walk you through some basic problems step-by-step.
That Massive Hay-wire that can be your electrical system can be conquered.  We will begin simple and work our way up.
Let's begin with the basics.  Your Boats Electrical System will usually consist of a battery, switch panel with several fuses and switches or circuit breakers, and then the devices to be powered (in this case we will be testing a Cabin Light).

You will find that the wires may be different colors from the colors used for automotive wiring.  Main Power Feeds are Red.  Negative Grounds are Yellow or Black.

Fuse & Switch Panels

In most cases the Fuse & Switch Panel has two purposes.

1) To protect a circuit from overloading.

2) To turn off or on a particular circuit.

Typical Circuits with Switches & Fuses are:

The Main - is a master switch and fuse for protecting and controlling all other circuits.

Accessories - This circuit is for all electronic equipment, radios, stereos, GPS's etc.  The fuse is generally much larger than what is needed to protect an individual piece of equipment.  Therefore there is generally an in-line fuse on each piece of equipment.  This fuse is a much smaller value than the Accessories Fuse and is intended to protect the piece of equipment.

Cabin Lights - This circuit is for all Cabin Lights.  In addition there is usually a switch at each Cabin Light for individual control.

Running Lights - Turns on and protects the bow lights, stern light, and tri-color mast light.

Steaming Light - Turns on and protects the Steaming Light which is a forward facing light about half way up the mast to tell other boaters that you are under power and will be obeying the normal rules for right-of-passage.

Spreader Light - Sometimes located beneath the Steaming Light or hanging from one of the spreaders.

Fans/Vents - Controls and protects any powered vents.

Anchor Light - a 360 white light mounted at the stern, amidships, or on the top of the mast.

Bilge Pump - This should be a unique circuit that is connected directly to the battery with its own fuse and control panel.  The idea being that if anything goes wrong with the Main Fuse Panel the Bilge Pump with still (hopefully) operate.  We will talk more about the Bilge Pump in a later section.  If you are interested now then follow the lilnk Bilge Pump.


A Basic Circuit - The Cabin Light Circuit

Let's look a basic circuit for a Cabin Light.  I have taken out the Mains Fuse and Switch to simplify the example.


As you can see in Figure 1 the open switch prevents electrons from flowing in the circuit.  In Figure 2 electrons can flow because

the switch closed and therefore the light bulb lights.

What Can Go Wrong

There are 4 basic things that can go wrong with your electrical system.

1) A dead battery.

2) A dead device. (Burned out light bulb.)

3) An open circuit.

4) A shorted circuit.

Always start by checking the battery and examining the failed device.  Check to see if the device's connectors are firmly attached and that the individual fuse (usually an in-line fuse) is not blown.  (In a later course we will discuss in-line fuses and their pitfalls.)

Beginning Check List

1.  Check the battery with a voltmeter.  It should read close to 13.8 volts.  Most electronic equipment will stop working or at the very least give you a warning if the battery voltage drops below 12 volts.  Volt meters can be very in-expensive.  I've seen them for as little as $3 at places like Harbor Freight.  An in-expensive one is all you'll need.

2.  Check the power connections and the device under test.  Make sure that it is firmly attached.  Try replacing a light bulb if that is what you are trouble shooting.

3.  Inspect the in-line fuse if there is one.  Sometimes this fuse is located very close to the device but sometimes it is several feet or more away.   So look around carefully.  I have seen in-line fuses install behind the Main Fuse Box, so look there as well.

4.  Digging a  Little Deeper - If you have determined that the battery is at full charge, the connector is firmly attached and the in-line fuse is in good shape it's time to dig a little deeper.


A) The Open Circuit

One thing that can go wrong with our basic circuit would be an Open Circuit.  An Open Circuit occurs when there is a break or Open somewhere in the wires, switch, or fuse.

Figures 3, 4 & 5 show several types of Open Circuits.



Trouble Shooting an Open Circuit

With the use of a simple 12 volt Circuit Tester you can look for and find an open circuit.  A 12 volt Circuit Tester is simple to understand and use.

You can use a voltmeter instead of a Circuit Test but a Circuit Tester is much easier to use.  There is a small lamp that illuminates which quickly tells you if power is present at the point under test.


We have listed a good Circuit Tester under Fun Gizmos.
We think it would be a good addition to any sailor's tool box. 
Figure 6 show a simple Low-Voltage Tester.  You should always test the Tester before you begin trouble shooting a circuit.  Take a look at Figure 7 to see how to check out the Tester.


Notice that the lamp lights regardless of which terminals of the battery you connect to.  My Circuit Tester cost only $4 at Harbor Freight and has a nice long (5 foot), heavy duty cord and cable clamp.  There are cheaper tester around but be aware:  They often have short, flimsy cords and clamps.

Types of Open Circuits

We will now take a look at each of the three types of Open Circuits above and see how the Low-Voltage Tester would help us figure out what has gone wrong.

1. Blow Fuse

Let's start with the blow fuse example.  You cannot always tell if a fuse is blown  by examining it.  Some fuses have very small fuse links.

We will begin testing the Positive side of the Cabin Light so start by clamping onto the Negative Terminal of the Battery.  Now touch either side of the fuse with the Tip of the Tester.  If the fuse (or circuit breaker) is blown the Tester will light on only one side of the fuse.  See Figures 8 & 9 below.



Replace the fuse.

2. Bad Switch

Yes, switches do go bad.  Often you can feel a change in the action of the switch but sometimes it appears to act and sound normal.

If the we suspect a bad switch then we need to test on either side of the switch.  Before you begin testing make sure the switch is in the on position.  See Figures 10 & 11 below.  Once again if the Tester lights on one side of the switch but not the other then the switch is defective and must be replaced.
3. Break in a Wire

A break in a cable can occur in either the Positive Red wires or the Negative Yellow (or Black) wires.

Red Wire Open Circuits

Suppose we check the point show in Figure 8 but the Tester does not light up.  First we should wiggle the connections at the battery and the fuse.  If either falls off they we need to re-attach and test again.

If both connections appear good then we need to test the wire.  Pierce the Red Wire close to the fuse and see if it the Tester lights up.  If not, then you must work your way toward the batter until you find the break and repair it.  You can similarly test the other Red Wires.


Yellow (or Black) Wire Open Circuits

What do we do if we've tested up to this point and everything appears okay but the circuit still does not work?

We would have to re-arrange our Tester so we can look for a break in the Negative Yellow (or Black) side of the circuit.  Take a look at Figure 13.  First move the Tester's Clamp to the Positive Terminal.  Next carefully pierce the Negative wire as close to the load (In this case our cabin Light Bulb) as possible.  If the Tester does not light than the problem is closer to the battery.  If the Tester does light up then it is most likely the Cabin Light Socket is defective.
Finally try testing the Negative Wire close to the battery (such as in the fuse box).  If the Tester lights up at this point than there is a break in the Negative Wire somewhere between the two points tested in Figures 13 & 14.  Keep probing along the wire until you find the break.

How Do Breaks in Wires Happen?

Breaks in wires usually occur where they connect to a device, at splices, or where they have been pinched.  Wires can be pinched where they pass around structural parts of the boat, near hatches and hinges, or when they pass through compartments where heavy objects might be stored.  The biggest culprits are crimp splices, in-line fuse connections, and terminal screws.

About Blown Fuses

It is important to note that fuses usually blow for a reason.  If you determine that the cause of the circuit failure is a blow fuse it is a good idea to visually inspect the fuse box wiring and the Circuit in question (in our example the Cabin Light Fixture) to make sure there is not a short in the circuit.

We will discuss how to find a short circuit in a following section.

A Few Words About the Switch & Fuse Box

In reality the Switch & Fuse Box is more complicated than what we looked at in the examples above.  Figure 15 show a partial diagram of a typical Fuse Panel.  As you can see in reality there are many more wires and connections to check while trouble shooting a Circuit.  This can be further complicated by the addition of indicator lights.


If you keep in mind the trouble shooting techniques we went over in the beginning of this course you will be able to progress through each section of a circuit and locate an Open Circuit.


B)  The Short Circuit


A Short Circuit occurs when any parts of a circuit comes into contact with any other part of the circuit.  As the name implies in a Short Circuit the electrons are taking a shorter path then was intended.

To trouble shoot a Short Circuit we must divide the Circuit in question into several sections, in others words we must artificially create Open Circuits.  We can do this by removing a Fuse, Opening a Switch, or removing a device, such as our Cabin Light.  The Low-Voltage Circuit Tester works on Open Circuits.  So if we create an Open Circuit we can look for and find a Short Circuit.

If you feel confused at this point don't worry.  We will go over how this concept works.  Let's look at Figure 2 again.

This circuit works because the Light Bulb limits the flow of electrons to keep the current below the rating of the fuse.

Let's look at two situations where a Short Circuit is present.  Figure 16 shows a Short Circuit at the Cabin Light Fixture.  Once again we are looking at a greatly simplified Circuit. I have taken out the Mains Fuse & Switch to cut down on confusion.  We will discuss a more complete Fuse Panel in a later Section.
Remove the Fuse and turn off the Switch.  Attach the Circuit Tester as shown in Figure 17.
If the Tester lights than the short is above the Blue Dotted Line.  If the Tester does not light then the short is below the Blue Dotted Line.  Move the Tester to the new point shown in Figure 18.

Now we must carefully inspect the areas where we think the Short Circuit is and remove the offending Bad Connection. 


Keep in mind that when we were testing in Figure 17 the problem may be in the Cabin Light Fixture its self and not just the wires connecting to the Fixture.

To find this out remove the Cabin Light Fixture completely from the circuit and see if the short goes away.  Look at Figures 19 & 20.

If the Short Circuit is in the Light Fixture then when the Fixture is removed the Short should go away and the Tester Light should go out.  See Figure 20.



Finally disconnect the Tester, remove any shorts, replace the blown Fuse, and turn on the Switch to see if everything works as expected.  See Figure 21.

If everything works okay, pat yourself on the back and go have a beer!  Job well done.

(Don't forget to turn off the Cabin Lights or you will have another electrical problem to deal with...a dead battery! lol:)


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