of the pickup coil 22 one end of coil 22 is positive relative to its other end thus the output voltage applied to pulse modifier 23 reaches a positive level of x volts at some point in time prior to the time at which the tooth 114 reaches a position about six degrees ahead of direct alignment with core 115 of the pickup coil 22 in the run mode the output signal of pulse modifier 23 is delivered to run amplifier 24 which responds by delivering a rectangular output voltage pulse rai run amplifier 24 turns on to initiate pulse rai at the instant the output signal of pulse modifier 23 reaches the level of x volts and it turns off to terminate pulse rai as the output signal of pulse modifier 23 falls below this level the output of run amplifier 24 is delivered as an input signal rai to timer 25 timer 25 produces a positive rectangular output voltage pulse tmi which is initiated at the leading edge of input signal rai and is terminated at the end of a fixed time interval thereafter with the proper operation of pulse modifier 23 in the absence of sensor signals pulse tmi will be terminated at all engine speeds just as tooth 114 reaches the point about six degrees ahead of direct alignment with core 115 of pickup coil 22 this time relationship is achieved through the action of pulse modifier 23 in appropriately shifting its output voltage relative to ground as engine speed varies pulse tmi from timer 25 is delivered to the control terminal 65 of switch 26 and causes switch 26 to be turned on during the constant time interval of pulse tmi.