Ok, having stock setup system ( coil feeded from ballast )and the signal required is just a trigger to turn on the system the SAFER and easier way to get power on both stages is get that signal from blue circuit before the ballast, the same used for the ECU and regulator. No need for extra relays with this.

Even is true this circuit is feeded directly from ign switch just on RUN ( ign1 ) getting 12 volts, while cranking is also sourced from the opposite side of ballast coming from Ign 2 circuit, being the ballast the splice, getting together both circuits, although getting a dimmed power while cranking ( 4-9 volts ) on run circuit. That voltage rate should be enough to keep on the EFI system working whil cranking IF is true the source you need is just a trigger on signal.

If this wasn't posible, the ECU will never be sourced while cranking either, so engine would never start

AAAAND that's why the cluster brake light dims out while cranking, because this bulb is feeded from same run ( ign 1 ) circuit BUT ign 2 coming out from the oposite side of ballast.