I don't know if this insight helps with your swap and what-not, but some position switches are open until selected, then closed and others are closed until selected, then open. So, you are getting the opposite. A standard position switch is just like a light switch, either providing continuity or not. I would guess the difference is in the signal sent/ received between the two. I don't understand (nor have I looked into) how an Auto Inhibitor switch works. I don't think you'd want to add any grounding to either wire. I'd take a closer look at the FSM for both the manual and Auto and see how they work a bit better, then proceed with modification.