Hey how do the 4 point harnesses connect to harness bars that mount behind the headrests?

 

The harness doesn't actually mount to the bar, It just rests over it and keeps the weight/pressure off of the back of your seat.

To mount the harness, you'll have to drill holes in your floor (if still using the back seats),........Mount the harness to the rear bolts that hold your drivers seat down, or take out your rear seats and bolt the harness to the 2 14mm bolts that hold the rear seat buckles down.

Here's pics to kind-of show the finished product.
http://www.lokarmotorsports.com/harnessbar.html

I'll see if I can get better pics for ya