1988 GMC Sierra wanted start

Engine Mechanical problem
1988 GMC Sierra V8 Two Wheel Drive Automatic

engine turn getting gas no spark changed rotor, coil, plugs, cap, ignition mod and still no spark even checked fuses. What can it be had once sparked but only once from coil just to to the plugs even new wires all the stuff is new. They is 4 wires going to the ignition coil the book said 1. Ground 2.? 3? 4 is 12volt when checked 12volt no power