Very suspicious, copper worm???

Hello, everybody.
today the situation:
I wanted to leave the V8 on after longer service life, nothing happened, battery empty. All right, a little bit surprised, but nothing more thought of, loading garage, done.
However, the electronic charger didn't want to, because electricity was still being used, so I turned keys around and pulled them off.
Suddenly, the horn honks for "to make out light". Looked, but the lights were off. So keys back in, turned back and forth, same problem still. Also try the light switch.
Now, however, the horn went out immediately if the ignition lock was in position 1 for the radio, but the control panel from the radio had not even on it. So, radio out, cable off, then the haunted thing was over. Cable back in, no more problems.

What's the connection? I guess that's why the battery was empty.

Greeting Florian