It may be just a blown fuse. In the high heat, sometimes they just give up.
I don't have a Ford chassis any more so I don't know the fuse location. Look in your Ford Operator's Manual for the fuse locations.
I believe the high speed is on a separate fuse from the lower speeds and that could be why high speed still works.
Suggest fixing the typo in the subject line so folks can find this topic in a "dash air" search.
Good luck,
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Partmgr, a job well done. thanks for the tip on the resistor as you were right on. $10 and 15 minutes later I have the blower working which is good at 113 degrees in Phx. This site and the Winny site make is easy to fix a lot of small things like I had. Partsmgr gives me the direction, I go to the on-line parts manual, get number then parts. All that is left is a little manual labor.
thanks again to all that responded.