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 TM 9-8000
and collapse as the contacts are closed and opened is
illustration are the means of opening and closing the
obvious. For example, when the contacts are closed, a
contacts and the means of distributing the induced high-
magnetic field builds up. This magnetic field moves
voltage surges from the secondary to the spark plugs in
across the second (or secondary) winding when it builds
the various cylinders. An actual diagram of an ignition is
up. This induces a voltage in the secondary winding so
shown in figure 15-3. Note the functions of the various
that a current flows through it and through the lamp. If
components in the system.
the lamp is of the right size, it will light up momentarily
b. Battery. The battery and generator furnish the
because the magnetic field does not take long to build
up.
source of voltage and current for the ignition system.
The battery is required when first starting, but, after the
(2)
When the contacts are opened, the
vehicle starts moving, the generator takes up the ignition
magnetic field collapses and again moves across the
load.
secondary winding, inducing a voltage that causes the
c. Ignition Switch (Fig. 15-4). The ignition switch
lamp to flash momentarily.
enables the driver to turn the ignition on for starting and
(3) With a capacitor (fig. 15-2), the lamp would
running the engine and to turn it off to stop the engine.
be brighter as the contacts opened. The reason for this
Most modern configurations of ignition switches
is that the capacitor speeds up the magnetic collapse.
incorporate four positions that serve the following
The lines move faster across the secondary winding in
functions.
collapsing because of the capacitor effect. Faster-
moving lines mean a higher voltage and more current,
(1) Off. The off position shuts off the electrical
which, in turn, means a brighter light.
system. Certain systems such as the headlights usually
are not wired through the ignition switch and will continue
to operate.
15-3.
Ignition System.
(2) Accessory. The accessory position turns
on the power to the entire vehicle electrical system with
essentials of an ignition system. Not shown in the
the exception of the ignition system.
Figure 15-3. Typical Automotive Ignition System.
15-4
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