Some of the earlier Ranger manuals have a Neutral Sensing Switch input to the ECA (aka computer, ECM or PCM). On the Mitsubishi transmissions, the NSS is behind the shifter. The Reverse Lamp Switch is on the passenger side of the trans case.
BTW, it's not a good idea to blindly apply voltage. In the case of the Neutral Sensing Switch, that power went directly to the ECA regardless of which wire was powered. Hopefully it wasn't damaged.