the best place for the power cable it thru the throttle cable hole as with the 2.2 there's no cable so its a spare bung that can be used but be sure to silicone the cable to the bung to stop you or the passenger from getting wet feet 🙂
the standard cable has been fine it my install with a 50w RMS amp powering the speakers in the car for many years
edit:- here's a pic of my 0 gauge cable as an example
