Again, I have not studied a wire diagram.
Typically the coil is switched on and off by the ground side of the circuit. The ground side is controlled by the switch mechanism (points on an old car, ignition module on middle aged cars, and ecu on a new car). So if the ecu is unplugged, the ecu is not grounding that side of the circuit. If by touching the power side of the circuit, the spark fires, you by default have to have a always grounded situation in the ground circuit. Remember that a coil fires when the field is built up (power and ground are applied) and fires when the field collapses (either power or ground is removed). If both power and ground are constantly applied, the field never collapses and you never get spark. This is basic high school automotive theory 101.
I would look for a ground circuit that has a pinched wire someplace on that coil.
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