O.k. a pretensioner is what's connected to that cable you dissconnected from the seat (that black cable with the red/black plug in your pictures above). Now dissconnecting this, u will have a little annoying light come up on your dash, flashing. U could take the bulb out, but what's the point? If you have a smash, then the pretensioner (the thing that looks like a shot gun barrel on right side of the driver seat and left of the passenger), will not fire and pull your seat belt tighter making u safer.
Basically, if u fit these brackets that u have made, u might risk failing the M.O.T. (not sure what u guys call it, but its the test ur car goes thru every year making sure the car is safe), and u've basically turned ur car into a Rally car! :lol:
Now what u could do is look at where the barrel connects to the seat itself (which I believe is a sticky out bolt thing). U can see it here...
Now all you need to do is make a bracket pointing upwards from the seat frame you've made. Basically its all straight forward, just copy what u see in the pic above and it will work...remember to plug the pretensioner in of course! :D
Otherwise, have a look at the pics on this topic so u can have some other ideas...
http://www.focuscanada.net/forum/index.php...opic=7874&st=20