XXXXXXX,
The flashing light indicates there is a concern in the transmission control system and it has stored a trouble code. This could be an electrical concern or a mechanical concern. You will need to have the codes retrieved and then a diagnosis of the code to determine the issue. Basically this light flashing is just like the check engine coming on for the engine control system indicating a malfunction. Let me know if you need more information.
Thanks,
Tim
Ford Technician
23 years Dealership experience, Ford Senior Master Technician since 2000, ASE Master since 1985