I still need some help, what do you mean by "Vertex attach cable model at point A", can I just move the origin point of the cable to the point A or do I have to 'attach' the cable to point A (how)?

Get direction vector, how do I do that?

For movement of the liftcar and counterweight I use;
....
while (elevator.z > floor1)
{
elevator.z -= elevator.z_speed * time;
conterweight.z += elevator.z_speed * time;
...

How does the cable scale itself with the used movement?

Regards,
Frits