I've tried holding the glow-plug down longer, but I still can't get it to fire. As the battery has run down in subsequent attempts, I first put a battery starter on it, and then attempted to jump the tractor from my car. In both cases, the battery doesn't seem to be helped much. But it still turns a bit. It just doesn't fire. There is plenty of fuel in the tank.
I don't know enough about diesel engines to know what to do next. What do you advise?