2003 Chevy Monte Carlo. The battery went dead. Replaced and the new one drained. Here are the symptoms: no start/not even a crank won't jump start. Clicking relays from the fuse panel, dash panel flashing, speaker static.
Here is what I tried:
Disconnected both battery terminals and used test light and discovered dead short. I traced it to the main wiring harness leading into the cab of the car (not the one leading to starter or alternator) I took out all the fuses one at a time and then the relays one at a time and the test light stays on.

How should I proceed and where can I find a complete car wiring diagram? Also, could the ignition be at fault?
Thanks in advance for any ideas.