Insignia 2.0 cdti 09 starting electric issues

[smokydiesel]

Hi guys hoping someone can help me with this insignia i have.
First off ive rebuilt the engine new crank and all the bottom end. Ive had it running but have a issue with the dash panel and satnav screen.
When they are dull the car just tuns over and doesn't fire put also you can let go of the key and it still keeps cranking?
But when the screens are bright it fire's up like it should do
I've had some mobile diagnostics out and there baffled.
Ive also tried another lockset the screens was nice and bright. But unfortunately i found out it's not that simple as my car doesn't have a electronic handbrake and the lockset came from a car with it.
I've heard it could something to do with the bcm. But id rather figure something out before I start throwing more money on it.