2004 Lincoln LS V8. Diagnosed a bad ECU. Installed new ECU. I’m aware of having to take it to the dealer to have it flashed. Will I get absolutely no response from turning ignition key to on position? When I hook up battery all I get are headlights that stay on. No dash lights or anything else. No response from key.

SOURCE: 2004 Chevy Tahoe Ignition is Off, Radio, Windows, Dash stay on

it needs to go to a dealer or mechanic as anything involved with the ignition is behind that area.

SOURCE: 2000 lincoln ls ignition key will not turn

try tapping the end of the key gently with a small hammer while trying to turn it this happens alot on Ford Escape and Focus

SOURCE: WON'T START..NEW BATTERY ..DEALER CANNOT DIAGNOSE

remove the sparkplugs and clean the heads with a wire brush and test to see if the gap is rite

SOURCE: 2004 lincoln navigator wont turn over. Had starter

have your battery and alternator tested. sounds like battery. No need to replace cable unless it is frayed or in poor conditin.

SOURCE: 2003 Lincoln LS V8, Won't turn over after errors

Forget the four coils. That is a common problem,but I would question 4 failing.
The ABS ,Parking Brake,Speedo Etc,where nothing to worry about,you were loosing power, when it went to fail safe,so they came up.

ETC -is Electronic Throttle Control, your problem? Maybe
You will need to have a scanner put on it's,daignostic connector under the dash,to check for codes. Them only a trained technician can follow a chart or test proceedure to properly repair.
I have a 2004 LS,one of Ford most high tech and complicated vehicles.
Conclusion: only a professional can repair you car.
I would start with a local shop. If money you have money to throw away,go to a dealer.
Most likely have to wave to it on a flat bed carrier. Don't flat tow it.