This is exactly the setup I have. Steel wire attached to the engine cylinder = pot. The clamp on the wire (not shown on the picture) is the slider. I can regulate the current on the glow plug from 1.9A to 3.2A (for the engine startup). However it needs about 3A to start. After that I can drop the current because burning gasoline adds the heat to the glow plug. I will know much more when I tune up the engine, so I can vary the temperature and see how does it affect the performance.