12 Volt direct drain electrical problem

Can you try to help solve a 12v direct drain electrical problem? I just got this car it was was sitting over 30 years. Previous owner put a fuel pump and tank in it. He couldn't get it running. I believe he seriously overcharged it. The new battery he bought went bad. The alternator diodes were shorted. After repairing the alternator I still have a 12v drain. The ignition switch or starter isn't shorted. If I unplug the ignition switch it goes away. There's a wire that's hot after I plug in the switch that goes to a grey? Junction box? About at the top of the dashboard looking from below. Any ideas what that is? I know Cadillac was the testing grounds for new things. I have never seen this and it has weird pronglike plugs.