The screen sounds like it either has a dead short, as it is clicking off like that, or the TIMER is at fault, the front screen are normally on a timer, this may be the other "relay" that you mention, if so try another from a scrappy, or pm me and I'll tell you how to bounce contacts to see if it is that.
The footwell lights are operated from same trigger as interior lights, so assume the interior light was on as well ?
The rev counter just stopped working, welcome to ford ownership
The headlights, you are probably correct about it being a duff relay, as they get a signal when ignition is on, relays do this sometimes.
All manner of odd seemingly unrelated problems occur on cars due to a BAD EARTH, single biggest cause of car problems lecky wise, so have a good clean at the same time, all the earth points you can find, particularly around battery area.
tabetha