BEFORE you start pulling fuses and opening up the power feed circuits to the
radio, I suggest that you know first how your radio will respond.
On many new vehicles, if you remove the battery feed to the radio, it will go
into THEFT mode, assuming that it is being stolen. When you return the power
feed to the radio, it will require you to enter the security code to get the
radio to function again.
There are other ways to carefully measure the power drain without opening up
the power feed circuits.