I have a 99 windstar that flashs the O/D OFF light on the instrument panel. Seems to do it after it has been driven 25 kms or more. Might be temp dependent.Doesn't seem to affect the way it drives and goes away each time it sits over night. Don't know what causes it.
There are about 50 things that can go wrong in the trans and make the OD light flash. The flashing light means there is a problem with the trans system and a code to explain the problem has been stored in the computer's memory. You MUST have the codes read to fix the problem. The places that advertise that they read codes free don't have the right tools to read Ford trans codes. You'll need a good independant shop or a Ford dealer.