Switched live

i dont think so, there maybe a switch live when you turn the radio on (amp in boot)

what is the ignition live needed for

or you could run a wire from the fuse box to the rear
 
can sort you out a split charge relay, works of a live feed then senses when the car is running, then when car is switched of it senses the voltages drop and shuts of, we use them on towbar wiring