See Figures 1, 2 and 3
With the ignition switch in the RUN position, the primary circuit current is directed from the battery, through the ignition switch, the ballast resistor, the ignition coil (in the positive side, out the negative side), the ignition module and back to the battery through the ignition system ground in the distributor. This current flow causes a magnetic field to be built up in the ignition coil. When the poles on the armature and the stator assembly align, the ignition module turns the primary current flow off, collapsing the magnetic field in the ignition coil. The collapsing field induces a high voltage in the ignition coil secondary windings. The ignition coil wire then conducts the high voltage to the distributor where the cap and rotor distributes it to the appropriate spark plug.
A timing device in the ignition module turns the primary current back on after a very short period of time. High voltage is produced each time the magnetic field is built up and collapsed.
The red ignition module wire provides operating voltage for the ignition module for the ignition module electronic components in the run mode. The white ignition module wire and start bypass provide increased voltage for the ignition module and ignition coil, respectively, during start mode.
The distributor provides a signal to the ignition module, which controls the timing of the spark at the spark plugs. This signal is generated as the armature, attached to the distributor shaft, rotates past the stator assembly. The rotating armature causes fluctuations in a magnetic field produced by the stator assembly magnet. These fluctuations induce a voltage in the stator assembly pick-up coil. The signal is connected to the ignition module by the vehicle wiring harness.
The occurrence of the signal to the ignition module, in relation to the initial spark timing, is controlled by centrifugal and vacuum advance mechanisms. The centrifugal advance mechanism controls spark timing in response to engine rpm. The vacuum advance mechanism controls spark timing in response to engine load.
The centrifugal advance mechanism varies the relationship of the armature to the stator assembly. The sleeve and plate assembly, on which the armature is mounted rotates in relation to the distributor shaft. This rotation is caused by centrifugal weights moving in response to the engine rpm. The movement of the centrifugal weights change the initial relationship of the armature to stator assembly ahead of its static position on the distributor shaft. This results in spark advance. The rate of movement of the centrifugal weights is controlled by calibrated springs.
The vacuum spark control mechanism can provide spark advance if a single diaphragm assembly is used or spark advance and retard if a dual diaphragm assembly is used. The diaphragm assembly used depends on the engine calibration.
The single vacuum diaphragm assembly also varies the armature to stator assembly relationship. In this case the stator assembly positioned is changed by means of vacuum applied to the diaphragm assembly. The diaphragm assembly is attached to the stator assembly by the diaphragm rod. The stator assembly is mounted on the upper plate assembly. The vacuum applied to the diaphragm and attached diaphragm rod to move, compressing the advance spring, which controls the rate of spark advance. The rate of spark advance is controlled by a calibrated spring.
Spark advance is obtained with a dual diaphragm assembly in the same manner as with a single diaphragm assembly. In this case, vacuum applied to the vacuum advance port cause the advance diaphragm rod to move, other wise the action is the same. Spark retard is obtained by applying vacuum to the vacuum retard port. This causes the retard diaphragm to move, compressing the retard spring, which controls the rate of spark retard. Compressing the retard spring allows the diaphragm rod stop to move due to force applied by an advance spring pushing against the it by means of a diaphragm rod. The result is the diaphragm rod moves, causing the attached stator assembly to change position with respect to the armature. In this instance, the direction of the stator assembly movement is opposite that occurring during vacuum advance, resulting spark retard. It should be noted that vacuum applied to the advance port overrides any spark retard caused by vacuum applied to the retard port.