I offer the following just for learning points, to figure out your problem the steps already posted are adequate.

Realize a diesel engine works because it creates so much pressure on the fuel that the fuel explodes. A gas engine fires a spark to ignite fuel.

I think there's two problems with the spark plug. A) a glow plug is meant to warm the engine/combustion chamber to help create more pressure, not cause combustion on it's own. B) You have no way to suppy power to a spark plug.

It ain't gonna work. GP's may run after startup but that's only to add heat to the chamber, not to actually combust fuel itself.

Good luck,
Bill