Remove the blk/yel from the amphenol connector at the powerpack and see if you regain spark.
If you do, you have a short in the blk/yel between the keyswitch and the powerpack or a defective keyswitch or emergency stop switch.
Another means of troubleshooting the boatside wiring is to connect a different control box to the engine and re-test though this may not be an option for you.
Unfortunately, unless you find a shorted component on the boat side wiring or a broken lead in the engine harness, you will need the use of a special tester (peak reading voltmeter) to check cranking output on the stator, timer base, and powerpack.
They cannot really be tested without the use of this meter.
If you are a betting person, I would try a new powerpack first.