Major problems. Please help?

I have a 1990 Honda Prelude SI. And the tach, speedometer, and odometer do not work. As for the odometer and the speedometer, i kbow those are both possibly realated to the speed sensor, but, ive been reading on the internet that even when you change the speed sensor, or cable it still does not work so thats not an option any ideas? And then the tach i have not a clue whats goin on there! Please any help would be appreciated!