I have had two 99 F-150's and both trucks have had the same problem so I am assuming this is a common problem on the 99 F-150 and maybe more models. I am surprised there hasn't been a recall. I have had this truck since 2003 and it always had this problem. I never fixed the problem on my first truck too.
The odometer will be on sometimes and off sometimes. There is no pattern and no trick to get it to turn back on, it just has its own mind. Even when it is off, it still adds up the milage. Does anyone know a simple fix? I asked my mechanic and he said the only way he knows how to fix it is to replace the entire gauge cluster but I don't want to make a big project out of it.

 

There is a sticky in the Electrical Forum.
Here is the thread...

https://www.f150online.com/forums/el...er-repair.html

 

Perfect instructions for the fix. I hope it isn't as hard as it looks. Thank you very much. Did you do this repair too??