I also have a D-19 (deisel). I have also done a lot of farming with D-17s. The comments on the Power Director, and Traction Booster are correct. If you do any heavy tillage work with it, all you have to do is move the Traction Booster lever forward on the column. Set your depth with your remote arm lever.
The tractor originally came out with a posative ground electrical system. Yours has had some type of conversion to negative ground.You might check under the gas tank where the electrical panel is and see if the regulator is there. If it charges, it may be that it is not disconnecting through the key switch. I converted my tractor over to an altenator and am pleased with it. Hope this helps.Mark