Hvacman

Bought another (relatives got my other 3) clean hi mileage ‘96 4x4 sr5 5 speed man. 5VZE California 4 runner. Been wrenching and fixing things. Runs good.
issue is when manually engage 4wd (doesn’t have the limited button) the dash light just flashes for a second and then is gone.
Crawling around underneath I see this spot for an electrical plug near the tail shaft. Think its a speed sensor, but speedometer works so not sure what it does?
where would the other end of this wire go? Thanks