I'm working through multiple issues on a recently acquired Williams Suspense. The bonus unit seems to be missing a wire on one of the switches. I find no loose/cut or unconnected wires anywhere. Based on a pic it looks like there should be a yellow wire on the post. Can anyone confirm the missing wire and where the other end of it should go?

After cleaning the bonus unit it will increment bonus points but when the ball drains no bonus points are awarded. Not sure if this is related to the possibly missing wire.

IMG_2048 (resized).jpg

Thanks. Bonus works just as stuliss and Mikala described. Somewhere in my research I found a pic that seemed to show the wire from the post attaching to a screw on the bonus unit itself (similar to a ground wire I guess). Since things seem to be working correctly I'll forget about the missing wire for now.
Thanks.