The Electrical System (An Overview)
When the automotive industry
was in its infancy, it used electricity only to ignite
the fuel inside the engine. By the late 1920's, the
electric starter replaced the hand crank, electric headlights
made acetylene lamps obsolete and the braying of the
electric horn drowned out the squeak of the hand-squeezed
air horn. Today, an automobile requires an elaborate
electrical system of circuits just to produce, store,
and distribute all the electricity it requires simply
for everyday operation.
The first major component
in the electrical system is the battery. The battery
is used to store power for starting, and for running
auxiliary devices such as clocks, radios and alarms
when the engine is off. The next major component is
the starter motor, which is used to start the engine.
The third component is a charging device powered by
the engine, known as the alternator. It powers the electrical
system when the car is running, and restores the charge
within the battery. With these basic components, the
car maintains its supply of electricity. A device called
the voltage regulator keeps the power level stabilized,
and the fuse box keeps minor problems from becoming
Many different auxiliary
electrical devices are used in modern cars, such as:
radios, cellular phones, rear window defrosters and
electric door locks, as well as a vast array of motors
powering everything from the moonroof on down.
The car's initial source
of electricity is a battery, whose most important function
is to start the engine. Once the engine is running,
an alternator takes over to supply the car's electrical
needs and to restore energy to the battery.
A 12-volt storage battery
consists of layers of positively and negatively charged
lead plates that, together with their insulated separators,
make up each of six two-volt cells. The cells are filled
with an electricity-conducting liquid (electrolyte)
that is usually two-thirds distilled water and one-third
sulfuric acid. Spaces between the immersed plates provide
the most exposure to the electrolyte. The interaction
of the plates and the electrolyte produces chemical
energy that becomes electricity when a circuit is formed
between the negative and positive battery terminals.
generator, or alternator, is the electrical system's
chief source of power while the engine is running. Its
shaft is driven by the same belt that spins the fan.
It converts mechanical energy into alternating-current
electricity, which is then channeled through diodes
that alter it to direct current for the electrical system
and for recharging the battery.
The automobile lighting
circuit includes the wiring harness, all the lights,
and the various switches that control their use. The
complete circuit of the modern passenger car can be
broken down into individual circuits, each having one
or more lights and switches. In each separate circuit,
the lights are connected in parallel, and the controlling
switch is in series between the group of lights and
the fuse box. The parking lights, are connected in parallel
and controlled by a single switch. In some installations,
one switch controls the connection to the fuse box,
while a selector switch determines which of two circuits
is energized. The headlights, with their upper and lower
beams, are an example of this type of switch. Again,
in some cases, such as the courtesy lights, several
switches may be connected in parallel so that any switch
may be used to turn on the lights.
The main lighting switch
(sometimes called the headlight switch) is the heart
of the lighting system. It controls the headlights,
parking lights, side marker lights, taillights, license
plate light, instrument panel lights, and interior lights.
Individual switches are provided for special purpose
lights such as directional signals, hazard warning flashers,
back up lights, and courtesy lights. The main lighting
switch may be of either the "push-pull" or
"push-pull with rotary contact" types. A typical
switch will have three positions: off, parking, and
headlamps. Some switches also contain a rheostat to
control the brightness of the instrument panel lights.
The rheostat is operated by rotating the control knob,
separating it from the push-pull action of the main
When the main lighting
switch completes the circuit to the headlamps, the low
beam lights the way for city driving and for use when
meeting oncoming traffic on the highway. When the dimmer
switch is actuated, the single filament headlamps go
"on," along with the high beam of the two
filament headlamps. The next actuation of the dimmer
switch returns the headlighting system to low beams
only on the two filament lamps. Some cars are equipped
with an electronic headlight dimming device, which automatically
switches the headlights from high beam to low in response
to light from an approaching vehicle or light from the
taillight of a vehicle being overtaken. The dimmer switch
in the automatic headlamp dimming system is a special
override type. It is located in the steering column
as part of a combination dimmer, horn, and turn signal
switch. The override action occurs when a slight pull
toward the driver on the switch lever provides high
beam headlights regardless of the amount of light on
For some years there has
been discussion about the advantages of a polarized
headlight system. Such a system comprises headlights
which produce polarized light in a particular plane.
The windscreens of all cars would be fitted with polarizing
glass, which would be oriented so that glare from an
approaching vehicle would be essentially eliminated,
while the forward vision would still be kept at the
present levels. The advantages the system appear attractive,
but the practical problems of making the transition
are very great, since it would not be practical to convert
all existing vehicles to this type of lighting. Also,
any benefits would only be marginal because glare itself
is not a frequent cause of accidents. However, many
cars now have refracting or colored glass to cut down
Due to recent legislation,
newer cars in Texas with the dimmer switch mounted on
the steering column will have to be refurbished with
standard floor-mounted dimmers. Too many Aggies are
being found in the ditch with their legs caught in the
The directional signal
switch is installed just below the hub of the steering
wheel. A manually controlled lever projecting from the
switch permits the driver to signal the direction in
which he wants to turn. Moving the switch handle down
will light the "turn signal" lamps on the
left front and left rear of the car, signaling a left
turn. Moving the switch upward will light the turn signal
lamps on the right (front and rear), signaling a right
turn. With the switch in a position to signal a turn,
lights are alternately turned "on" and "off"
by a turn signal flasher. Incorporated in the directional
signal switch is a "lane change switch mechanism."
This feature provides the driver the opportunity to
signal a lane change by holding the turn lever against
a detent, then releasing it to cancel the signal immediately
after the maneuver is completed.
In order to signal a stop,
a brake pedal operated "stoplight switch"
is provided to operate the vehicle's stop lamps. In
addition to lighting the conventional rear lights, the
switch also operates the center high-mounted stop lamp,
that became mandatory on later models. Cruise control
equipped vehicles may also utilize a vacuum release
valve. In this case, both the vacuum release valve and
the stoplight switch are actuated by movement of the
The car horn on passenger
cars provides the driver with a means of sounding an
audible warning signal. The horn electrical circuit
generally includes: battery, fuse or fusible link, horn
relay, horn(s), steering column wiring harness, horn
switch, and body sheet metal. Often, a cadmium plated
screw is used to ground the horn to the body of the
vehicle. Horns usually are located in the forward part
of the engine compartment or in the front fender well.
The horn switch is built into the steering wheel or
incorporated into the multi-functional switch lever,
which includes turn signal and dimmer switch.
The ancient Greeks had
a word for it. Records show that as early as 600 BC
the attractive properties of amber were known. Thales
of Miletus (640-546 BC), one of the "seven wise
men" of ancient Greece, is credited with having
observed the attraction of amber for small fibrous materials
and bits of straw. Amber was used by these people, even
as it is now, for ornamental purposes. Just as the precious
metals had their names of gold and silver, so amber
had its name: "electron." It was later shown
that the same effect can be obtained by rubbing a rod
of glass or hard rubber with a handkerchief. Many other
nonmetallic materials are found to have this property,
which is known as "static electricity."
All electrified materials
behave either as glass or rubber. Glass has a "positive"
charge and hard rubber has a "negative" charge.
If you electrify two strips of hard rubber by rubbing
them with fur, they will repel each other. Two glass
rods will behave the same way. But, if you electrify
a rod of rubber and suspend it near an electrified rod
of glass, they will attract each other. One of the most
important laws of electricity is "Bodies with similar
charges repel each other; bodies with opposite charges
attract each other." A positive charge is designated
with a (+); a negative charge by the sign (-).
Although people have controlled
electricity for many years, no one can explain exactly
what it is. Many different theories have been given
as to the nature of electricity through the years, but
the modern one is the "Electron theory." In
short, the electron theory proposes that all matter
consists of tiny particles called molecules. These molecules
are made up of two or more smaller particles called
atoms. The atoms are then divided into smaller particles
called protons, neutrons, and electrons. These particles
are all the same in matter, whether in gas, liquid,
or solid. The different properties or characteristics
of the matter take form according to the arrangement
and numbers of these particles which make up the atom.
The proton has a natural positive charge of electricity;
the electron has a negative charge; and the neutron
has no charge at all, but just adds weight to the matter.
Protons and neutrons form
the central core of the atoms about which the electrons
rotate. The electrons carry small negative charges of
electricity, which neutralize the positive charges of
the protons. The simplest atom of all is the hydrogen
atom. It consists of one positive proton and one negative
electron. Other atoms, such as those forming copper,
iron, or silicon, are much more complicated. Copper,
for example, has 29 electrons circling about its nucleus
in four different orbits. While protons are much smaller
than electrons in size, they contain the bulk of the
mass of every atom. One proton, for example, weighs
nearly two thousand times as much as an electron. The
electrons therefore are light particles or objects around
a small but relatively heavy nucleus.
It is difficult to conceive
the size of the atom. Research by physicists has established
that the mass on one electron is about .000,000,000,000,000,000,000,000,000,911
of a gram. If you assume that one proton in a hydrogen
atom is the size of a baseball in Kansas City, then
the electron would have an orbit which would reach from
the Atlantic coast to the Pacific. Along with the extremely
small size of electrons and protons, they are separated
by relatively vast distances.
Not all substances are
good conductors of electricity. As a general rule, metals
are good conductors whereas nonmetals are poor conductors.
The poorest of conductors are commonly called "insulators,"
or "nonconductors." Aluminum, copper, gold,
iron, mercury, nickel, platinum, and silver are examples
of good conductors. Amber, glass, mica, paper, porcelain,
rubber, silk, and sulfur are all nonconductors. The
difference between a conductor and an insulator is that
in a conductor, there are free electrons, whereas in
an insulator, all of the electrons are tightly bound
to their respective atoms. In an uncharged body, there
are an equal number of positive and negative charges.
In metals, a few of the electrons are free to move from
atom to atom, so that when a negatively charged rod
is brought to the end of the conductor, it repels nearby
free electrons in the conductor, causing them to move.
They in turn repel free electrons in front of them,
giving rise to a flow of electrons all along the conductor.
There are a large number of substances that are neither
good conductors of electricity nor good insulators.
These substances are called "semi-conductors."
In them, electrons are capable of being moved only with
some difficulty, i.e., with considerable force.
In Motion (Electrical
When an electric charge is at rest it
is spoken of as "static electricity," but
when it is in motion, it is referred to as an "electric
current." In most cases, an electric current is
described as a flow of electric charge along a conductor.
To make an electron current flow continuously along
a wire, a continuous supply of electrons must be available
at one end and a continuous supply of positive charges
at the other. This is like the flow of water through
a pipe: to obtain a continuous flow, a continuous supply
of water must be provided at one end and an opening
for its escape into some receptacle at the other. The
continuous supply of positive charge at the one end
of a wire offers a means of escape for the electrons.
If this is not provided, electrons will accumulate at
the end of the wire and the repulsion back along the
wire will stop the current flow.
The rate at which the free electrons drift
from atom to atom determines the amount of electrical
current. In order to create a drift of electrons through
a circuit, it is necessary to have an electrical pressure,
or "voltage." Electric current, then, is the
flow of electrons. The more electrons in motion, the
stronger the current. In terms of automotive applications,
the greater the concentration of electrons at a battery
or generator terminal, the higher the pressure between
the electrons. The greater this pressure (voltage) is,
the greater the flow of electrons.
In modern electric car designs, the drive
motors are often used as the brakes also, allowing them
to switch over into performing as generators, which
charge the batteries with the energy generated.
The connection between electricity and
magnetism was made by Oersted, a Danish scientist, in
1820. He had frequently demonstrated the nonexistence
of a connection between electricity and magnetism. His
usual procedure was to place a current-carrying wire
at right angles to, and directly over, a compass needle
to show that there was no effect of one on the other.
One occasion, at the end of his lecture, he placed the
wire parallel to the compass needle and saw the needle
move to one side. When he reversed the current in the
wire, the needle, to his amazement, deviated in the
opposite direction. Thus a great discovery concerning
electromagnetism was made quite by accident.
There is no actual knowledge as to why
some materials have magnetic properties and others have
not. The "electron theory" generally is accepted
as the best explanation of magnetism. It is also known
as the "domain theory."
According to the theory, an electron moving
in a fixed circular orbit around the proton creates
a magnetic field with the north pole on one side of
the orbit and a south pole on the other side. It is
assumed that the orbiting electron carries a negative
charge of electricity, which is the same as electrical
current flowing through a conductor. Current flow, then,
is from negative to positive. When a number of magnetized
orbiting electrons exist in a material, they interact
with each other and form "domains," or groups
of atoms having the same magnetic polarity. However,
these domains are scattered in random patterns throughout
and the material is, in effect, demagnetized. Under
the influence of a strong external magnetic field, domains
become aligned and the total material is magnetized.
The strength of its magnetic field depends on the number
of domains that are aligned. In magnetic substances,
the domains align themselves in parallel planes and
in the same direction when placed in a magnetic field.
This arrangement of the electron-created magnets produces
a strong magnetic effect.
If you stroke a piece of hardened steel
with a magnet, the piece of steel itself will become
a magnet. (Steel railroad tracks laid in a north-to-south
direction become magnetized because they lie parallel
to the magnetic lines of the earth.) Much stronger magnets
and magnetic fields can be produced by electrical means.
Placing a piece of steel in any strong magnetic field
will cause it to become magnetized.
A magnetized field surrounds any conductor
carrying an electrical current. The discovery of that
fact resulted in the development of much of our electrical
equipment. The "field of force" is always
at right angles to the conductor. Since the magnetic
force is the only force known to attract a compass needle,
it is obvious that a flow of electric current produces
a magnetic field similar to that produced by a permanent
magnet. Not only is the field of force at right angles
to the conductor, but the field also forms concentric
circles about the conductor. When the current in the
conductor increases, the field of force is increased.
Doubling the current will double the strength of the
field of force.
Left-Hand Rule (Magnetic Effect)
Oersted's experiment has been interpreted
to mean that "around every wire carrying an electric
current there is a magnetic field." The direction
of this field at every point, like that around a bar
magnet, can be mapped by means of a small compass or
by iron filings. If a wire is mounted vertically through
a hole in a plate of glass or other suitable nonconductor,
and then iron filings are sprinkled on the plate, there
will be a lining-up of the filings parallel to the magnetic
field. The result shows that the magnetic lines of force
or "lines of induction" are concentric circles
whose planes are at right angles to the current.
The "left-hand rule" used in
electromagnetism can always be relied upon to give the
direction of the magnetic field due to an electron current
in a wire. Derived from experiment, the rule states:
"if the current-carrying wire were to be grasped
in the left hand, the thumb pointing in the direction
of the electron current, negative (-) to positive (+),
the fingers will point in the direction of the magnetic
Properties of A Solenoid
Shortly after Oersted discovered the
magnetic effect of a current-carrying wire, Ampere found
that a loop or coil of wire (a single loop or a coil
of several turns of wire) acted as a magnet. A coil
of wire of this kind is sometimes referred as a "solenoid,"
or as a "helix." The magnetic lines of force
in a solenoid are such that one side or end of the coil
acts like a "N" magnetic pole and the other
side or end like a "S" magnetic pole. At all
points in the region around a coil of wire carrying
a current, the direction of the magnetic field, as shown
by a compass, can be predicted by the left-hand rule.
Inside each loop or turn of wire, the lines point in
one direction, whereas outside they point oppositely.
Outside the coil, the lines go the same way they do
about a permanent bar magnet, whereas inside the coil
they go from "S" to "N". Not only
does one coil of wire act like a magnet, but two coils
will demonstrate the repulsion and attraction of like
and unlike poles.
Electronics refers to any electrical component,
assembly, circuit, or system that uses solid state devices.
"Solid state" means that these devices have
no moving parts, other than electrons. Examples of solid
state devices include semiconductor diodes, transistors,
and silicon controlled rectifiers. These and many more
have broad application in automotive electronics.
Semiconductors are made from material
somewhere between the ranges of conductors and nonconductors.
Semiconductors, basically, are designed to do one of
three things: (1) stop the flow of electrons, (2) start
the flow of electrons, or (3) control the amount of
electron flow. A semiconductor diode is a two-element
solid state electronic device. It contains what is termed
a "P" type material connected to a piece of
"N" material. The union of the "P"
and "N" materials forms a PN junction with
two connections. The "anode" is connected
to the P material; the "cathode" is connected
to the N material. A diode is, in effect, a one-way
valve. It will conduct current in one direction and
remain non conductive in the reverse direction. When
current flows through the diode, it is said to be "forward
biased." When current flow is blocked by the diode,
it is "reverse biased." When a diode is reverse
biased, there is an extremely small current flow; actually,
the current flow is said to be "negligible."
When the P and N are fused together to form a diode,
it can be placed in a circuit. The P material is connected
to the positive side of the battery and the N material
is connected to the negative side of the battery. Connected
in this manner, current will flow. If connected in the
reverse manner, current will not flow.
A transistor is a solid state device used
to switch and/or amplify the flow of electrons in a
circuit. A typical automotive switching application
would be a transistorized ignition system in which the
transistor switches the primary system off and on. An
amplifying application could be in a stereo system where
a radio signal needed strengthening.
A transistor is a three-element device
made of two semiconductor materials. The three elements
are called "emitter," "base," and
"collector." The outer two elements (collector
and emitter) are made of the same material; the other
element (base) is different. Each has a conductor attached.
The materials used are labeled for their properties:
"P" for positive, meaning a lack of electrons.
It has "holes" ready to receive electrons.
"N" is for negative, which means the materials
has a surplus of electrons. The movement of a free electron
from atom to atom leaves a hole in the atom it left.
This hole is quickly filled by another free electron.
As this movement is transmitted throughout the conductor,
an electric current is created from the negative to
the positive. At the same time, the "hole"
has been moved backward in the conductor as one free
electron after another takes its place in a sort of
chain reaction. "Hole flow" is from positive
to negative. Current flow in a transistor, then, may
be either electron movement or hole flow, depending
on the type of material, and this determines the type
of transistor it is as well.
In most 12 volt systems, a resistor is
connected in series with the primary circuit of the
ignition coil. During the cranking period, the resistor
is cut out of the circuit so that full voltage is applied
to the coil. This insures a strong spark during cranking,
and quicker starting is provided. The starting circuit
is designed so that as long as the starter motor is
in use, full battery voltage is applied to the coil.
When the starter is not cranking, the resistance wire
is cut into the circuit to reduce the voltage applied
to the coil. If the engine starts when the ignition
switch is turned on, but stops when the switch is released
to the run position, it can indicate that a resistor
is bad and should be replaced.
At no time should the resistor be bypassed
out of the circuit, as that would supply constant battery
voltage and burn out the coil. The resistor and resistor
wires should always be checked when the breaker points
are burned, or when the ignition coil is bad.
Information Systems, Inc.)