glow plug light

Hi, Still kinda new to the forum so hope this is posted in the correct place.

I just collected my 2000 Fabia last night, 1.9 sdi engine.

Anyway, when the engines been running for about 2-3 minutes on idle, or about 15 seconds if you give it revs, the glow plug light stays on.

i had a quick search on here and found out about brake switch, but the brake lights seem to be working ok so i dont think its that, Any idea what the problem could be?

also if anybody has done any of these before, let me know how hard they are to do!

i need to replace the track rod ends, wishbone bushes, a broken heater vent, fuel filter and take off the tow bar!

Thanks for any replies