Coil Off Condenser Ignition switch Coil On Condenser Ignition switch Figure 4-16.  Typical ignition switch in on position.  Figure 4-15.  Typical ignition switch in off position.  this chapter. Some ignition starter switches have a push to  prime feature during the starting cycle. This system allows  additional fuel to spray into the intake port of the cylinder  during the starting cycle. Figure 4-15  shows that the primary current is not interrupted  when the breaker contacts open since there is still a path to  ground through the closed, or off, ignition switch. Since  primary current is not stopped when the contact points open,  there can be no sudden collapse of the primary coil flux field  and no high-voltage induced in the secondary coil to fire the  spark plug.  As the magnet rotates past the electrical gap (E-gap) position,  a gradual breakdown of the primary flux field occurs. But that  breakdown occurs so slowly that the induced voltage is too  low to fire the spark plug. Thus, when the ignition switch is  in the off position with the switch closed, the contact points  are as completely short-circuited as if they were removed  from the circuit, and the magneto is inoperative. High-tension system magnetos used on aircraft engines are  either single or dual type magnetos. The single magneto  design incorporates the distributor in the housing with  the magneto breaker assembly, rotating magnet, and coil.  [Figure 4-17]  The dual magneto incorporates two magnetos  contained in a single housing. One rotating magnet and a  cam are common to two sets of breaker points and coils.  Two separate distributor units are mounted in the magneto.  [Figure 4-18] When the ignition switch is placed in the on position, switch  open, the interruption of primary current and the rapid  collapse of the primary coil flux field is once again controlled  or triggered by the opening of the breaker contact points.  [Figure 4-16]  When the ignition switch is in the on position,  the switch has absolutely no effect on the primary circuit. Flange-mounted magnetos are attached to the engine by  a flange around the driven end of the rotating shaft of the  magneto.  [Figure 4-19]  Elongated slots in the mounting  flange permit adjustment through a limited range to aid in  timing the magneto to the engine. Some magnetos mount by  the flange and use clamps on each side to secure the magneto  to the engine. This design also allows for timing adjustments.  Base mounted magnetos are only used on very old or antique  aircraft engines. The ignition/starter switch, or magneto switch, controls the  magnetos on or off and can also connect the starter solenoid  for turning the starter. When a starting vibrator, a box that  emits pulsating direct current (DC), is used on the engine,  the ignition/starter switch is used to control the vibrator  and retard points. This system is explained in detail later in  High-tension ignition systems have undergone many  refinements and improvements in design. This includes new  electronic systems that control more than just providing  ignition to the cylinders. High-tension voltage presents  4-10 Magneto Mounting Systems Low-Tension Magneto System Single and Dual High-Tension System Magnetos 1.  Through the closed breaker points to ground and 2.  Through the closed ignition switch to ground.