As stated previously. Commonly black to ground. Red to 12volt switched power and the green to tach signal.
Is this what you did?
From what I can understand of your connections.your grounding the power and power to ground. Still dosent explain why no cranking. How did you determine what wires you spliced into?

From the directions i got they said to splice into the red wire coming from the ignition. I also unhooked what i did... still no cranking, its at the shop now.

Have you checked all the fuses? You're going to have to trace starter voltage, S terminal on starter, from the starter back through the neutral safety switch, ignition switch then fuse block or the other way around.

I am betting blown fuse. From putting ground to power. Be interested in hearing what your shop finds.

If the ignition is no longer hot when on then you more then likely just blew a fuse.

Is there a fusible link that he could have cooked by crossing the wires?

It's possible. I believe the main splice/distribution point on the 72 is from the starter. Battery cable to starter then I believe fusible link to main power feed. He should have absolutely nothing if he blew the fusible link. No lights, accessories, nothing.