Here's a simplified ignition system wiring diagram of the 1992, 1993, 1994 4.0L Ford Explorer and 4.0L Ford Ranger. You'll find part two in the next page.
The ignition system, on these particular vehicles, is a Waste Spark System. Which in plain English means that two cylinders get spark at the exact same time.
The ignition coil assembly, with its 6 towers, is composed of 3 individual ignition coils. Each ignition coil fires spark to two cylinders simultaneously.
I've written a tutorial that explains the on-car ignition coil test in a step-by-step manner. You can find it here: