Ok I played with you picture a bit hopefully you can follow it.

You should be able to just parent your geometry, but I would have to see a picture, its better than trying to get the AIM constrates working right.

Steps

1) Have your arm straight up

2) Pick joint 3 rotate it 90 degrees down than set perefered angle (right click on the joint)

3) Straighten up your arm again then add a ikSCsolver from joint 4 to joint 2

(Optional) depending on what you want the movement to be, you can set perefered on joint 2 as well.

That should do it. If you want to move the arm select the ik and test it, Just the joint 4 to 2 will move, If you want to rotate the base just select joint 1.

Hope that helps