Frank, you've posted several questions about this model, but it seems you're not telling us the result of this problem. You say the voltage is dropping below 12 volts with the glow plugs on. But does the tractor start? You say it's draining the battery within 35 seconds, a very long time to have your glow plugs on.
In general, 8-10 seconds of glow plug should be enough unless you're in VERY cold weather. Maybe 8-10 seconds two times, but never 35 seconds in a row.
Please let us know if the tractor is starting, and if so, is the battery coming back up. Ease off on those glow plugs. You seem a little obsessed about the voltage, and a couple of us told you in another post that everything seemed to be okay from the readings you told us. Good luck and let us know what's up.
John