MFA Problem

Following replacement of the ignition switch on my Rivage ( which is another story in itself) my MFA gives strange readings - e.g. temperature of -10 which I know is wrong as it rarely goes below freezing in Guernsey! Also MPG which looks too low, and engine temp. not coming on for ages and then not going over about 70, whereas it used to go up to 104, even with a maximum speed limit of 35 mph!

I tried disconnecting the battery overnight, as has been suggested on the Club GTI Forum. Any ideas?

Colin :?