The dominant method of providing spark on late model gasoline engines is coil on plug (C.O.P.) ignition systems. Looking underhood on different vehicle makes will reveal that some coils have 2 wires, some have 3 and others have 4. The presentation examines how each of these coils is triggered and what tools and test methods are best. Several scope images and component pictures are included. Also consider viewing the July 2011 article on this topic I wrote for Underhood Service.