I have a 1987 "Wrangler yj with a 2.5L 4 cylinder. I get no spark at all. I have replaced the ECU, coil, distributor, rotor. I have 12 volts coming into the coil at the yellow wire, 12 volts across the yellow and black. I am at a total loss. For a coil to work the 12 volt power must be disrupted. But on this model there is no lead coming from the distributor.