I have recently purchased a 1998 Mondeo. The Auto gearbox was faulty so I got the car at a good price. I thought I would do it up. The old gearbox that was faulty did not go into Drive, just 1,2 then drive when the speed was high enough. I got another gearbox out of a different Mondeo and put it in. All well and good for a few weeks, it worked sweet as a nut. Now I have the problem the the O/D light keeps flashing. I have no idea what this means but it seems to be intermittent. If I go over 50mph it will come on and the gear changes are "thumpier" than usual. It stays flashing for a while then it will go off. Going into 1st gear is the "thumpier" of them all when it is flashing. Eventually it will go off and the gears will return to normal smooth! I have also noticed that the fuel consumption has increased and I am not getting as many miles to the gallon. It is also a bit sluggish than usuall. I do not have anything to read the codes with and worried to take it into a garage because I'm sure they will charge me £££$$$££££. Has anyone seen this fault before? Any ideas on what I can do to rectify it. Any help would be appreciated as I am pulling my hair out.