Won't start one day and fires up first crank next day

Been learning myself for 40 years......

Make sure your ECU is grounded well.
-possibly bad connection at firewall

Do you have a voltage meter?

Dual ballast or single?

Also hot wiring to coil wont make it fire.... fyi you need voltage to ballast and ECU

This!!

First thing to check is to make sure ECU is grounded.