It is easy.
1) Take a 3/8" drive rachet and cheater pipe that fits over the end of the rachet.
2) Place the rachet drive into the auto tensioner with the rachet in the "off" position. There is a square hole in the auto tensioner arm for the rachet to fit in. Note routing of belt. There should be a diagram under the hood that shows the routing.
3) Put cheater pipe on rachet and pull. Slide belt off alternater pulley, and release the rachet slowly.
4) Remove old belt working it off the fan and out between fan and radiator. This is the hard part.
5) Place new belt on over the fan and route over all pulleys except alternater (equally hard as getting old one off).
6) Place rachet back in auto tensioner arm. Put cheater pipe back on rachet and pull.
7) Work belt over alternater pulley.
8) Release rachet slowly and remove.
9) Verify belt is in all pulleys correctly.
10) Crank truck and idle to make sure belt tracks correctly and does not jump off.
11) Enjoy a job well done.
