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TM 9-8000
Figure 15-4. Ignition Switch and Positions.
(3) Ignition On. The ignition-on position turns on
to do in the ignition system. First, it must close and open
the primary circuit to produce the magnetic buildup and
the entire electrical system, including the ignition switch.
collapse in the ignition coil.  Second, it times these
(4) Start. The start position will energize the
actions so the resultant high-voltage surges from the
secondary will be produced at the right time. Third, it
starter solenoid circuit to crank the engine.  The start
must establish a timing sequence to direct the high-
position is spring loaded to automatically return the
voltage surges to the proper spark plugs.
switch to the ignition-on position when the key is
(2)  The primary circuit through the distributor
consists of a set of contacts and a capacitor connected
d.  Ignition Coil.  The ignition coil consists of a
across the contacts. The contacts are closed by spring
primary winding of a few hundred turns of relatively
pressure and
heavy wire that is about 0.04 inch in diameter (no. 18),
plus a secondary winding of many thousands of turns of
a very fine wire that is about 0.004 inch in diameter (no.
38), both assembled around a soft iron core and
surrounded by a metal case topped with an insulating
cap that carries the terminals (fig. 15-5). Because the
countervoltage induced by the collapsing magnetic field
is about the same value for each turn, the ratio of 100:1
(100 turns in secondary to 1 turn in primary), the
secondary voltage could go 100 times as high as the
primary.  Because  the countervoltages induced in the
primary may reach 200 volts or more (by the rapid
collapse of the magnetic field brought about by capacitor
action), the secondary voltage could reach 20,000 volts.
This high voltage is carried through the ignition distributor
and distributed to the correct spark plug.
e. Ignition Distributor (Fig. 15-6).
(1) The ignition distributor has several jobs
Figure 15-5. Ignition Coil Construction


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