Obd2 scanner won't connect to ECU. I have no dash lights, headlights, brake lights, or horn among other things. All the fuses under the hood visually look fine. I hear a relay clicking maybe efi main? That's only when battery is unhooked for a short time and headlights and dash lights work for about 2 seconds. This happened after I shorted the factory amp connector :/
Also no crank or start

 

There are also fuse areas on driver and passenger sides inside. Passenger side above kick panel is the radio and probably amp fuse also. Sounds like more than just a fuse and it really depends on what you shorted out. Use a multimeter to diagnose.

 

Visually all the fuses are fine. Now I'm getting ZERO power to anything

 

I have same issue, no communication with ECU, only cooling fan runs with key turned to on position, cranks but no start, no CEL in display,fuel pump relay clicks when key 1st turned on

On drivers side, fuse block near battery , look thru plastic tops of fuses to see if blown, pay particular attention to 140 amp Alternator & 80 amp P/J, this is the fusible link

 

All fuses look good. Took 140a off and took cover off of it looks pristine. And so do the 80amps. Checked all the fuses of things not working. They are fine as well. Everything points to a fusible link, but they look fine

Mine won't crank or start and NOTHING works except a few dash lights cel etc

 

Without the ECU, the engine still can crank but no start.
What I worry about is that the ECU is not getting the power from the battery. Something must be stopping it. Judging from your words, "NOTHING works except a few dash lights cel etc", I suspect that the AM2 line of the ignition switch is not functioning.

 

I checked the am1 fuse it was fine. I'm going to start pulling all the 80a out next I guess. All of them look good from the top down. What is am2 line

 

Both AM1 and AM2 lines supply DC 12V to electronics controls. The AM1 line is getting the DC12V via the alternator 140A fuse. On the other hand the AM2 line is getting it directly from the battery.

 

Use a voltmeter as it is the simplest and best time consuming way

 

I have codes B1261 Engine ECU communication stop and B2620 ECU power source. I found this online for B2620... see if this helps

 

So me installing the amp and it popping apparently was just a coincidence. Battery ended up being dead and having some kind of short internally. Thanks for everyone trying to help. New battery and I'm good. And the amp and sub still work. 🥂