2001 SuperDuty is like the 97-03 MY F-150s, the switch has to be turned to the headlamp position, and pulled out to activate the fog lamps.
Page 26 of your owners manual shows the usage of them.
In case you got short changed on the owners manual, you can download a PDF version from Ford.
https://www.fleet.ford.com/maintenan...ls/default.asp
Not sure if the ramp mod like the F-150 is the same as the switch for the 2001 SuperDuty line, for being able to turn the fog lamps on with the parking lamps only ( and they stay on with the high beams ).
The Yahoo site from FedEx Pilot is now down ( he warned about this ~ 3 years ago ), so the searches for
fog light mod might point to this URL. Think there is another site that has the directions also, search would point to it, maybe use advanced search for the term, and ascending in the display options ?