I'm not sure how the turbos work but on the Cossie the alternator signal wire to the battery light on the clock also earths out the relay for the heated screen so you can't turn on the heated screen unless the car is running.i know this because i spent hours trying to diagnose why my heated screen wasn't working and then read somewhere the car had to be running before it would work lol .I think this was to prevent flattening a battery if the car wasn't running