I've got a similar problem - glow plug light flashing on/off for the duration of the journey, but unlike the above, my brake lights are fully lit all the time (even when the engine is off!!)
Any idea how to deal with this so that it doesn't discharge the battery overnight?
Torque (via ODB II ELM327 reader) reports no fault codes (even while the glowplug light was flashing away to me...)