Just fitted my new kenwood single din stereo half canbus 04 plate signum

Engine on: it works ok and when driving it seems ok, but when stationery engine still on if i turn the steering wheel its cuts in and out as if the powers not getting through.If i rev the engine and turn the wheel its works ok though.

Then engine off and ignition turned to position 1 it stays on for 10 to 20 seconds then starts to cut in and out again as if theres a power problem.

Oh wise ones please help