Mondeo Tdci 130 Estate 2003 - Warning Lights + Speedo And Rev Counter Not Working

Hi guys - new on here and desperate for some help.

My wife has a 2003 Mondeo TDCi Estate which she has owned for a couple of years and its been a brilliant car, never had a problem until about a month ago when the following happened.

Warning lights appeared on display for EMS, Battery, Glow Plugs and Outside Air Temperature, the heated front screen was inoperative and the computer / odometer displayed just a series of dashes.. This lasted a few miles and then all was back to normal again, but only for a day or so and then the warning lights came back on again. This continued to happen for a few weeks then in addition the rev counter and speedo stopped working and the problem now seems to have become permanent not intermittent, I also noticed that there was a fan noise coming from the intercooler area (i.e. not the main cooling fan) which lasts about 2 minutes after switching off. Today I removed the battery and checked the earth connections under the fuse box, I loosened the screws / bolts and retightened them. Having done this on reconnecting the battery all was well - no warning lights, speedo and rev counter were working. I thought it was fixed but 5 miles later the problem is back - no rev counter no speedo and a dashboard that is illuminated like a Christmas tree. I have an MOT due in a week or so and I am concerned that it might fail due to this problem, especially the speedo not working. Any guidance would be greatly appreciated.

It seems that every time the battery is disconnected and reconnected it corrects the problem but only for a few miles.

Thanks

Mike