On my gtb machine the switch for the ball is open not closed unlike my Bally machines

goodolddays is correct, Gottlieb ball tilt is normally closed, the style of switch stack looks like it's open, but it you look closely you'll see that it is closed, and the leaf being moved by the ball opens the switch.

The slam and ball tilts are a common issue. These are meant to be normally closed, and don't rely on a visible inspection for that, I've seen them look fine but with dirty contacts failing to make proper conduct. If there are no broken wires, slide a business card between the switch contacts with some pressure on them to clean off any accumulated dirt, and then make sure they are closed.

You can solder a jumper to the cpu to remove these for ever as a problem, but that should only be attempted if you have the knowledge and skill to work on a board. More info here - http://www.pinrepair.com/sys1/index.htm#slam