I'm surprised the law hassled you in an ag state like indiana. Cop must have been a city slicker.
Did you pull it with a real truck or a pickup? The laws might be different between the two. I agree that most farm equipment is exempt but is it exempt only when transported to and from the field or any time it's on the road? If it was purchased at a sale and is being pulled home by a truck that's commercially licensed for over 26000 pounds it might have to follow commercial laws. I think the cop was following the book to closely, or interpreting the book wrong. Jim