I have an X3 Navigation radio, MKIV DVD and Flip Up Screen, connected these together with a retrofit harness on the workbench, connected the IBUS wire from the Radio but still there seems to be no power to the screen, radio plays and DVD powers up, all components were working in an X3, I do not have an X3 but want to fit the system to an old E28. Please I would really apreciate some help !!!