head unit only powers up for 2 seconds?

There will only be one live wire for that Audi as the original stereo is triggered using a digital signal, u can connect both to the perment but it's not great, u can use a product from connect 2 called a ignigen which will trigger when the alternator is running to create a fake ignition wire, alternately u could use the cigarette lighter or go to the fuse box and use an empty accessory socket on the fuse box, make sure u use a fuse inline as close to the source as u can !!!!!!!D6-In Car Solutions

Thanks mate, got the head unit back yesterday & wired the baby in by just using snipped wires & insulation tape. Everything's working ok so I,ll nip out & get a fuse lead & some connector blocks later. 

Thanks for taking the time to reply.