Ignition Control Module: Description and Operation

Fig. 113 Power Transistor And Ignition Coil:

The power transistor, located on the front of the left strut tower, is a low current switch. It allows the signal sent from the ECU (very low current) to activate the primary circuit in the ignition coil (much higher current). This induces high voltage in the secondary windings of the ignition coil, providing spark to the distributor cap and plugs.