If it runs with the key in the start position, it runs. The failure to run in just the on position means it isn’t getting power anymore as his test proved. He doesn’t have it wired right.
Fix the wiring and then move on to diagnosing the fast idle condition. It is a compound problem that needs to be fixed one step at a time.
When people always go “Well first I did A, then B and now C is this...”, my first assumption is that A is wrong. No point is discussing further if A isn’t correct.
