Tilt Steering Kaput---89 F350

My tilt steering won't change positions (it used to be changeable when I'd push on the turn signal lever so the lever was moving away from the steering wheel). Now, the lever can be pushed but it doesn't seem like it's moving far enough..or where it is doesn't allow it to engage (or disengage) the tilt unlocking function.

Can someone explain what's going on (or what's supposed to be going on) deep inside, or better, explain it and suggest a place where I could find a schematic diagram.

Thanks. Dave