Wiring in an" ignition on" is for convenience, it has nothing to do with battery draining unless you accidently leave the HU on when you leave the car. When the HU is turned off manually then there is no current draw from the battery (just a miniscule 2mA or so to keep the memory alive, but this is needed whether you have an ignition on or not). You need to identify what is draining your battery, for that you need a multimeter. Remove the earth lead from the car battery, set the meter to amps and connect it between the earth lead and the earth terminal on the battery. This will then measure the current draw from the battery. When doing this do not turn the ignition on or try to start the car, just leave the keys out. What is the current draw at this point? It should only be about 50mA maximum, in order to drain the battery it will have to be a lot more. Pull the HU and disconnect the black power ISO plug, does this solve the problem? If it does then there is something wrong with your wiring. If the curren drain remains the same then it is not your HU causing it. Lock the car and see if it changes to eliminate the alarm. Then take out a fuse from the fusebox, if the current drops then the fault is with that circuit. If it stays the same then replace it and move on to the next fuse. At some point you will find the ciircuit responsible and then you can diagnose the fault. Common faults are alarm, handsfree kit etc or anything electrical that has been added to the car.
If you don't have a multimeter then buy one they are only £10.
