is thir any way to replace the stock s4 alternator with a one wire alternator? is so what does it invlove or can it just hook up

If you can get the alternator to line up with the properr pullies sure you can use one, but you will have to take out the idiot lights due to the fact they will always be on for the lack of the sence wire on the stock alternator. Not exactly bolt in but very doable. or you can go with a 3rd gen alt that should take care of all your problems.

why would you want to use a 1 wire alternator?

because it simpeler and more reliable