I’ve got an earlier 2007 radio in a Sierra that’s started giving issues. Sometimes it comes on when the engine is running, not with the ignition. Disconnect it when the engine or ignition is on and the radio turns on. Enter the code and it’s fine. Turn it off on the key and back on again and it’s not working again.

got ignition and permanent live and good earths and it’s doing nothing apart from lighting up when the headlights come on.

I think the unit may be at fault