No spark / No start

That's pretty good. The point you made about the "single ground" is good. Many wrongly think the coil and or distributor (breakerless) need grounded

Couple of minor points:

The ECU should not be powered off the coil side of the ballast but rather run direct to the battery. I don't even use a ballast for short tests, I just make sure not to leave the coil powered for long

It would be a good idea LOL, NOT to put the ballast on a plastic backing as shown.

You might have mentioned, or maybe I misunderstood, (some folks might not) that the test lamp is simply acting as a probe. I just use it sometimes because it makes a handy probe. Most of the time I try to find my Lisle spark tester, which is adjustable.