Each coil has has two wires from each ignitor. the black/white is positive and the yellow/ green is negative. both coils have this setup. on hte trailing coil negative side, there is a second wire that looks like a coax cable. I cant find it in the wiring diagram and I don't know what it goes to. Is this the tach drive wire?

 

The tach runs off the trailing negative side so that's a possibility.