It seems so simple if only two choices; I hate to mess up your diagnostics. Unfortunately there is at least one other possibility. That is the engine speed sensor.

The control unit uses the speed and cyl identification signals to control the timing of the coil field collapse. Have you checked current or voltage? Did the circuit open and close? The coil only makes a high voltage spark when its low voltage (high current) field collapses. Just running 6-8amps through the coil won't do anything but make it into an electro magnet.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician