Originally Posted by Billybob

Well actually based on the facts presented the only assumption you can make at this point is that the fire had some effect on the glow plug system. You haven't presented any facts as to the cause of the fire or even what was actually burning.

The glow plugs normally would only be energised and a potential source of heat and maybe fire when the vehicle was starting. In your case it sounds like the car had been running for a time and the fire/burning was noticed when you shut things down. From your description it does not sound like you thought the fire had been burning the entire time the motor was running?

I would look for what was actually on fire/burning first, eliminate any potential fuel for a fire, then look for possible sources of ignition, rectify that. Any chance that leaking injector return lines, delivery valves, injectors provided a source of diesel to burn? Any chance that there is some metal wire debris touching the glow plug wiring leading to a short that would produce a spark or burn?

Sounds like you may have burned up the insulation on the glow plug harness and now the circuit has shorted out the fuse in the relay, hence the failure to glow start the engine.