If your tractor is the same tractor as a Massey Ferguson 1010, when you turn the ignition key to the left, it will send current to the GPs as long as you hold the key in that position. And when you turn the key the other way to crank the engine, it will supply current to the GPs until you release the key. The light will stay on the whole time.
You need to test all 3 plugs to make sure they are good. Mine do nothing for 10 seconds. Use the GPs for 20 seconds even on a warm day and see what happens.
When I start my tractor, if it balks after starting, I turn the key back to the left as it is running and that provides a little extra heat to the cylinder until the exhaust clears up.
Parts are drying up on the Massey 1010. But I've been able to get what I needed for mine. There are sources that Massey doesn't even know about because the tractor was sold under several different brands.
Best of luck and enjoy your tractor.