have a look for a little plastic plate where a light unit would fit in.

Theyve done this on loads of fords where some ghia or something has the light but nothing else

I dont have focus 2004 on wiring diagrams but i do have c-max 2003 1/2 and it shows glovebox lamp so you might be able to get parts off that if it isnt available for the normal focus. The parts just a simple plunger with a lamp holder.

The fiesta version looks like this:


it fits into a bracket like this:


It will likely be slightly different on later cars.