FORD 2001 F-550 v.1 - Manual (Page 117)

The SuperCab rear seat has three straps behind the top of the seat back
that function as both routing loops for the tether straps and anchor
loops.
The tether strap anchors in your vehicle are in the following positions
(shown from top view):
Attach the tether strap only to the appropriate tether anchor as
shown. The tether strap may not work properly if attached
somewhere other than the correct tether anchor.
• F—Series Regular Cab
• F—Series SuperCab
• F—Series Crew Cab
Seating and safety restraints
117