I had to do that on my Almera as I amped up my standard stereo, I would advise against doing it like that if your headunit has a dedicated remote wire output.it is a live switch wire
put it to the ignition live wire,,,,,,,,,,,,,then a switch between that and amp if you want
What make of headunit is it? I know the Pioneer units I've had all have it coming out of the loom that they come withSo if there is an option to do it in the back of the stereo do that? will it be in the little plastic wiring box thing that comes of the stereo or actually on the head unit? Will any small current wire work, just twist/solder/tape the ends on?