Step 1. Place the pre-tensioner under the cable. Lift it up so the cable slips into the channel. The all-thread that extends beyond the housing should be facing the end post, with the back side of the pre-tensioner butted up against the last intermediate post in the rail (not the end post itself).
Step 2. Clamp the correctly-sized locking pliers to the cable, so the shaft beyond the thread fits into the counter-bore in the locking pliers.
Step 3. Lock the pliers.
Step 4. Using a 3/4" wrench on the wrench flat of the all-thread, rotate the all-thread counter-clockwise, tightening the cable to the desired level of tension.
Step 5. You may now connect your cable at the last post (end post), without having to pull tension through the entire cable length, just from the pre-tensioner to the end post. When you have finished installing the cable at the end post, release the locking pliers, remove the pre-tensioner, and move on to your next cable, repeating the process.