i really wouldnt power it just from the ignition! its not supposed to be like that, the ignition switch might give up, that wouldnt be good, my mates mk2 did this,it might not but its quiet likely i would say. i wouldnt use the stereo at all, or ever take your car to halfrauds, they dont have a clue, could you not find a blown fuse as this is probably where the wire is 'broken' the wire cant have just broken.