My 2.0 mondeo is just the same. I turn off ignition, wait a few seconds then turn ign. back on and nearly always glow plug indicator is then OK. This maybe happens about once a month. If it comes on after starting, engine knocks like hell, so I stop car, wait, and then restart, this has only happened VERY occasionly. Couple of years ago light came on whilst driving, lost power, light would not go out and couldn't restart engine. That cost me about £700 for a diesel pump overhaul. Light still sometimes gives problems though. Cars eh!
Terry Western, October 2010