2003 freight liner columbia electric problems

My truck has no power inside the cab there is no power in fuse panel main wires. Batteries show 12.5 volts check engine and engine protect is on even with out the key. When i turn the key nothing happens nothing lights up. It seems like there is a short somewhere i i will be checking it tomorrow with voltmeter any one got any ideas where to start ? does the main power goes to ECM first then it sends to everything else ?

I should add that truck worked fine before it went bad after i turned it off and tried to turn on again all i would hear is click click like the starter is bad but all my lights would be flashing when cracking on and off and now it is completely dead batteries still show 12.5

 

I did check two fuses that are in there and they are all good the weirdest thing that happened was when the truck had any power and cranking by clicking my APU started cranking which would not be possible as APU has its own separate electronic starter so i disconnected my APU power and it was able to ge the truck started but check engine would go on and off temperature gauge was at 0 my fan would go on and off and then the truck would have no pulling power then get it back and this was going on and off until i stoped

 

Ok i got the power back bad connector at starter truck started. But now i got all kinds of signals check eng on temp warning light comes on and off with fan running oil pressure is over 60 which cannot be no power at pulling shows max 10 psi off boost

 

I think maybe my ECM got damaged 4 pins to it got 12.6 volts and one pin shows 4.6 with ignition on and 1.4 off so ecm gets power i am getting 10 codes faults