Ford 2003 Mustang Workshop Manual page 2030

All engines
6. Rotate the belt tensioner and position the accessory drive belt aside.
7. NOTE: The procedure listed below can be carried out on any of the 4.6L engine accessory drive
belt idler pulleys.
Remove the bolt and the belt idler pulley.
8. To install, reverse the removal procedure. Refer to
in this section, for accessory belt routing.
Accessory Drive or Accessory Drive—Cobra