This should be relatively simple to troubleshoot.
Disconnect the negative battery cable and place an ammeter in series with the cable and the battery. If you see a drain with the key and all accessories turned off (don't forget to close the doors and trunk) which you probably will, then start removing all the fuses while watching the ammeter. When you pull a fuse that makes the ammeter go to zero, you've found the circuit. Even before pulling a fuse, I would remove the radio wire you were talking about and see if that is the culprit. If it is, the ammeter will go to zero.
Somewhere there is something on, or shorted causing the drain. By monitoring the drain while you disconnect things, you will find the offending circuit.