Power for underseat subwoofer

[tomnetwork]

Upgraded the head unit, dash Speakers, and door Speakers in my 2009 aygo and I'm now looking to add an under seat subwoofer like this to give it some more bass.

I understand that there will be 2 connectors from the head unit for the audio, and then 3 connectors for power, one going to the positive terminal on the Battery, one going to ground, and a negative connection.

However for the negative connection I wouldn't want to connect this directly to the Battery as it would constantly draw power and drain the Battery.

Does anyone know a good place I could connect this to which will provide 12v power only when the ignition is switched on? Or any other solutions which I am missing?

Thanks

[APS]

Ground IS negative. No need to run a separate cable.

[flash22]

3 wires are

12v - from the Battery and fused within 150 mm of the Battery

GND - Ground or Negative (connect this to a body ground/negative as close as you can to the Sub/Amp)

12v REM - this usually a thin blue REM or remote wire on an aftermarket radio to turn the sub/amplifier on/off