BATCamx7x

so i bought a new ecm thinking it was the issue. nope same thing no data link. the key will not turn it over before and after ecm swap it does try to start if i jump it from the starter i put in a new igniigtion switch but still wont try to start from key.. just bough a new obd plug to see if that would help havent installed it yet. also someone had cut the battery cables so i went to go puyt the new negative cable on and i have no idea where any of it goes and every diagram ive seen is crazy looking i need a dumbed down version the junction box confuses me too.

I have no Crank no start on ss Silverado 03 awd. I have 4 codes. Please help with any and all suggestions at this point I can't make it any worse. Cat Evap O2S HTR