V50 Electrics : Utilize 12v socket (and cable) to provide power to subwoofer

[Xariez]

Hiyya,

Back with a quite concrete question (for once) this time. As some of you may or may not know at this point, I got an aftermarket subwoofer installed in my V50 T5 -04. Up until now, the remote power (or "wake-up power signal") has gone through a button behind the waterfall console.

The other day, however, I got the (so far, untested) idea to take an old/used GPS, cut the end of the cable, and plug the positive/red side into the "remote" power (and the 12v plug to the 12v socket) to wake the subwoofer, when the 12v sockets receive power (which is when the car turns on). I am extremely close to trying this, but figured I'd ask around here first if anyone have tried this, or have any concerns what could, if so, go wrong? Or do we need to "hook on" the negative/black cable as well for the 12v socket to push any power through at all?

Thanks in advance!