If it's got a Jap Pioneer (Carrozzeria) unit fitted, then I'm assuming it's already got the fitting kit with separate A/C controls? If so, ditch the unit & replace with a NZ one, either a double din touchscreen (make use of the reversing camera), or a single din & a pocket. Most cheap $200-ish units have triple pre-outs, dual USB (front+rear), SD card, BT, front aux anyway... what more do you need?
Those Jap units seem to have a lot of wiring, for some strange reason too, maybe due to built in digital tv tuners, toll card readers, etc... I've ripped quite a few out in the past, not so much recently.