What exactly are you using for a test gap? For example if you are using the original coil high tension wire, it might just be that it's as simple as a bad coil wire!!
Also if you have not done so, I would "dewire" the system from the car until you get it fixed. That is, direct hotwire the system until you discover "is it" the ignition system, or "is it" the car wiring harness, etc?
Don't leave it powered for long while testing. You want to bypass the ballast that is connect all 3 circuits together and jumper power into it. As before, measure coil NEG and if it's a volt or two that tells you the ECU is conducting through the coil, which is good. Try again with the "tap" test, and finally if that part is good, "work" the dist. connector in/ out several times to feel for tightness and to scrub the terminals. Then spin the dist or crank it and see if you have spark at the coil