On the Ford diesels, the glow plug light is an engine management warning light which flashes to warn of a developing fault. The ECU then cuts the power to prevent engine damage.
You can read fault codes off the milage display but then you need the dealer to tell you what the code means...
To read the codes, hold down the trip reset button and the start the car. After about 5 seconds, you will see all the guages flick over to full deflection. Once it's in this mode, release your finger off the trip reset button and then scroll through the data readings by pressing the trip reset button. You're looking for a screen that says DTC on it. If there is no fault code, then is will flash up "none". If it has a fault code then it will flash up a number. If you don't have any codes there then I don't think you will have much choice but to get a diagnostic done on the car.
When you switch off the ignition it will exit the diagnostic mode and return to normal.