all the items you describe are controlled by the fuse box you have changed.The fuse box is also a control module when replaced it needs configuring to the car.What did Ford class as the body control module? as this fuse box controls alarm and locking functions.Where the corrosion was in the fuse box are the connectors that go there free of corrosion?
You need to start by making sure the fuse box is correctly programmed to the car,the remote locking function needs to be activated in the fuse box(module)as part of this.
start with one fault the heated front screen first. If the heated screen comes on by itself this is a protection feature for the charging system overcharging.
Check the charge rate of the alternator if it goes above around 15volts this would be seen as excessive so the fuse box (GEM) turns on the heated screen to try to use the excess.
Can you clarify what isn't working now?
It is possible an overcharge condition could cause the GEM to shut down. I still think this problem is related to the GEM as everything that isn't working is controlled by the GEM.
I would just check that the screen is actually working and it's not just the light on the switch that is on.
I have exchanged all of the relays on both fuse boxes with another focus just to make sure and no difference.
Have had the alternator checked and it was 13.90
Yes heated screen is definatly on.
Ford did fit a new GEM (fusebox) and programmed it and made no difference so they put the old one back in.
I have tried my fusebox (GEM) in another focus today and all the functions worked fine.
We have used a circuit tester on all the fuses on the GEM and did not get a light from the following fuses - 47(washer pump/heated washer jets), 63 (electric windows), 69 (foglamps) and 84(reversing lamp/electric mirrors)
So it appears that there is no power getting to these fuses
fuses 47,63,69 and 84 are all powered by the ignition relay in the fuse box next to the battery, this is switched by the GEM. The power from this relay is from fuse 25 (10amp)in the battery fuse box,when switched to earth the relay powers the fuses you have given from fuse 12 (40amp) in the battery fuse box. Check these two fuses and the relay operation, check you have 12 volts at two terminals of the relay pins 1 & 3 with ignition on. The relay is the 4th down on the right in the battery fuse box,there are three small relays above it and one small relay below it the ignition relay is bigger than these. Power from fuse 25 also powers the heated screen relay this is switched by the GEM.
If the fuses in the battery fuse box are ok you need to check for 12volts at pin 21 of connector 96 (green and red wire) of the GEM and 12 volts at pin 13 (black and blue wire) of connector 95 at the GEM.