IGNITION CIRCUIT COMPONENTS
Various ignition circuit components are designed
to achieve the functions of the ignition circuit. Basic
ignition circuit components are as follows:
BATTERYprovides power for the circuit.
(This was discussed earlier in this chapter.)
IGNITION SWITCHallows the operator to
turn the circuit and engine ON and OFF.
IGNITION COILchanges battery voltage to
high ignition voltage (30,000 volts and greater).
ignition voltage to the spark plug. Contains
either mechanical contact points or an electronic
SPARK PLUGdevice that provides an air gap
in the combustion chamber for an electric arc.
The ignition switch (fig. 2-43) enables the operator
to turn the ignition on for starting and running the
engine and to turn it off to stop the engine. Most
automotive ignition switches incorporate four
positions, which are as follows:
OFF.The OFF position shuts off the electrical
system. Systems, such as the headlights, are usually
not wired through the ignition switch and will continue
turns on power to the entire vehicle electrical system
with the exception of the ignition circuit.
IGNITION ON.The IGNITION-ON position
turns on the entire electrical system including the
START.The START position will energize the
starter solenoid circuit to-crank the engine. The
START position is spring-loaded to return to the
IGNITION-ON position when the key is released
The ignition coil (fig. 2-44) produces the high
voltage required to make current jump the gap at the
spark plugs. It is a pulse type transformer capable of
producing a short burst of high voltage for starting
The ignition coil is made of two sets of windings
(primary and secondary), two primary terminals (low
voltage connections), an iron core (long piece of iron
inside the windings), and a high voltage terminal (coil
The primary winding is the outer winding and is
made up of several hundred turns of heavy wire,
wrapped around or near the secondary winding. The
secondary winding is the inner winding and is made up
of several thousand turns of heavy wire located inside
or near the primary winding. The secondary windings
are wound in the opposite direction of the primary, and
the ends are attached internally to the primary
windings and the high voltage terminal. Both windings
are wrapped around an iron core and are housed inside
the coil case.
To obtain the high current required for ignition,
battery current flows through the ignition coil primary
windings producing a strong magnetic field. The
action of the iron core strengthens the magnetic field.
Figure 2-43.Ignition switch and positions.
Figure 2-44.Sectional view of an ignition coil.