2000 350 7.3 crusie control don't work. What could it be

 

The CC will not engage if either the foot brake, parking brake OR clutch switch are activated. For example if the parking break lever is not fully seated in the up position the CC won't activate. I'd check these things along with the fuse. But I don't know off hand if there is a fuse for the CC.
Eric

 

Failed brake pressure sensor. Had the same issue with my Freestar.

Here's a video from FordTechMakuloco on the issue.

https://www.youtube.com/watch?v=mICxnDTTIJI