Simple re-wiring
Take a test lamp, unhook the ground cable and hook the battery in series with the test lamp to ground.
Start pulling fuses one by one.
You have a modern stereo/ radio with "memory keep alive?" How about a separate high power amp?
If pulling the fuses doesn't drop the load, unhook the main alternator output stud. You might have a leaky diode, or the internal radio capacitor (condenser) may be leaky
What do you mean by "ignition switch wire?"