If the OD light is flashing there should be a DTC stored in the PCM memory. I would start by scanning the car for any codes.
2003 Mustang GT - All the usual engine bolt-ons, brakes and a road race suspension - SOLD
89 5.0 LX - Too much to list, goes fast, turns and stops!
1999 F-350 Modded 7.3L DIT