Now that the bracketry is set up, youll need to run the cable. The cable runs out from the inside, but before you pullup the carpet, youll need to knock the plate out of the floor board.
You can see the plate here on the left, right next to the exhaust pipe and between all those fuel lines. Its also almost directly across from the tailstock of the tranny, on the right.
To remove it, youll need to squeeze the tabs shut with a pair of pliers, then simply push the plate upwards with a large screwdriver. The top of it is sealed, so you might need to tap the screwdriver with a hammer to knock the plate loose.
If you have a 95+ truck, youll just need to remove the old cable from the hole at this point.