Even though the light is off current is maintained for several seconds and during cranking.So either you have one or more duff plugs or the normal fault on these which is the fuel filter assembly is allowing fuel to leak back into the tank due to faulty non return valve.take out the injectors and switch to glow plug start position,you will be able to see glow plugs down injector hole's and tell which if any are working.
caine
August 2008