I just did this last week, took me two tries to get it right. I wish my controller door didnt lock down or I could just open it up and look for you. But here is what I did, it might help you out:
I went to google and typed in imperial trackball schematic and also tried imperial trackball diagram and went through the results until i found a more or less good listing of which cords went where. The blue and brown are axes and so were the other two colors (orange and yellow? I think?)
I got it hooked up the first time and I got it almost right, moving the trackball up made the cursor move right and moving it right made the cursor move down. So I just flip flopped the x and y axes cords and bingo, worked on the second try.