My Focus has recently developed some kind of electrical fault, which I first noticed as flickering headlights, but it seems to affect all the internal lights and radio as well. The problem is intermittent, so I presume it's some kind of loose/dodgy connection. It went in for a service the other day, and I asked them to take a look, but they couldn't replicate the problem so they just checked the headlight earthing points, and nothing has changed. I noticed this morning that the courtesy light was flickering before I turned the headlights on. Also, a couple of times this morning, all my dials maxed out before going to zero, then returning to normal. Can anyone please shed some light on what's going on?
The main common link between all the things you have stated as being problematic is the battery. Interior lighting is on the ignition fuse (F8), the others are all on the main supply fuse (F7). Both these fuses are located in the engine fusebox. Both these fuses are connected directly to the battery positive terminal via the fuse box, so it could be a problem with the fuse box, the connection to the battery or the battery itself.
I have had the problem with all the dials reading maximum, returning to zero and then to normal a few times last winter - when it was cold, damp, used once a week and the battery was low. Once the battery was well charged and the weather turned warmer and drier things improved. The dials do this to re-calibrate themselves when a power failure has occurred. I'd check the fuses are securely fitted and are in good condition and then look at the battery and its contacts.