Put my mates focus in for a mot today and it failed on headlights not working properly he says it is doing the following
Turn dipped beam on they come on flick to main beam they come on ok but dipped beam does not stay on when main beam is on weird so i checked my focus and they work correctly any one on here had this before
Ford focus 2000 face lift version 2.0 ltr petrol

 

If its a 2000 focus its a pre facelift. If its got facelift lights in it the wiring from the switch needs modding to stop what you've described above.
I'll find ya a diagram...

 

http://www.focusowners.com/forum/vie...p?f=90&t=38435

there you go

 

If its standard and worked correctly before try swapping the stalk from yours and see what that does.
Thats just going off the top of my head and previous experience with similar happening on older Fords.May work,may not but the cost to find the problem would be zilcho

 

If its pre facelift there working correctly as they only have 1h4 bulb. So they switch between dipped and main. The facelift ones have 2 bulbs so dipped beam stays on when main beam is selected.

 

Cheeres for that daveysaff i take a look at that tomorow