I seem to remember there are some early Mk4's that were intended for TravelPro type radio satnavs rather than full screen displays. I think these may lack necessary display hardware. How old is your Mk4?

I'd reccommend reposting on the X3world nav forum - there are specialists there that can help. I think your problems are generic rather than X3 specific. It would seem that the ibus is connected and woking (screen opens when requested) but the video signals are not getting through to the screen.