Hi guys, now here's the story! So my son has bought a 2008 Audi A3 2.0 TDI 140 £1650 payed it's his first car and one he will be learning to drive in , so we go look at it of coarse it's been lowered and played with, the guy tells us the dmf has been swamped out for a solid fly wheel, I tell him that will need to be rectified which we will do.
so we're driving home and it drops into limp mode...gets home scans the ECU with vcds to discover it's over boosting, ok another task to add to the ever growing list.
So today my son comes to me and says can I fit your old S3 Audi nav unit in? Sure mate go ahead I was only going to throw it out eventually. So we're at the car takes the old head unit out (Audi concert) the car already had the connection for the GPS antenna and for the auxiliary port, so installs it, then he started the car (just because he can an it's his) 😂 ....so I said ok turn it off we're done...turns the ignition off ...the car is still running and the key in his hand.....so we stalled the car to stop it, then we tried to start it.....dash lights come on and go out as normal but she'll not turn over or even give signs of an attempt..... absolutely baffled.... although not scanned it since as the laptop needs a charge , but it will be scanned again in the next hour

Thanks for listening guys and I would appreciate any advice on this, I'm good with the mechanical side of things but electrical issues not really my thing.