[f5fstop]

Forgot you had the Z1, and you probably have the Z1 bypass too, and the relay provided with the periperal is turning on the pioneer, via a signal from the purple wire (class 2) into the peripheral adapter.
So, if you just want to cut the radio power, then a relay signaled from the starter system could shut off the radio.
If you abort the startup the radio will only stay on for ten minute before the BCM signals the peripheral to shut off the radio. This should not affect the battery, if that is the concern.