I just bought a new serpentine belt for my 1996 Mercury Sable DOHC
because my current belt is looking very cracked and old. I found
the diagram on the hood for the belt placement but I'm not sure on how
to replace the belt and tension it.. Can anyone steer me with
some directions?? Thanks!!

look for the spring loaded tensioner pulley, put a decent size wrench to it and that will give you the needed slack.

If you haven't done it yet replace the bearing in this tension pulley. The bearing in mine froze and broke the belt. Also be sure you have the right belt, but you will have to have the correct motor size to check this

there ara only two engine options for that year, the 3.0 Vulcan (crap) and the 3.0 24V Duratec (excellent). So tell your local parts guy which one you have and if you have a/c or not. Then you'll be sure you have the right belt.

THE TENSIONER IS LOCATED TOWARD THE BACK OF THE FIREWALL BETWEEN THE ALT AND THE CRANK PULLEY YOU WILL HAVE TO GET IT FROM THE BOTTOM GOOD LUCK