1991 Cadillac Deville no start/no crank

Well where to start 1991 Cadillac Deville 4.9 this issue came out of no where the car ran and shifted fine then the no start/no crank, I have replace the distributor, battery& terminals, the neutral safety switch, the bcm and ecm both used I have checked the key pelt and checked vats no security light( that I know of) but when I hook up a wire from the big yellow wire on the ignition switch (right at the switch) to another big yellow wire going out the firewall (right at the firewall harness)then the car starts and runs fine. So I must be bypassing something in that line, But no the trans wont shift automatically only manually and no first gear or over drive any ideas what this issue might be I don't mind rechecking any thing you can come up with thank you for your time-- Chet