Side note; when troubleshooting the reverse lights on my s14a, I found out that they get power from the gauge cluster circuit. So if your gauge cluster works... there SHOULD be power to that harness point. May just be a faulty switch.
What I did was pull the harness connector to the reverse light switch and try to short it, manually, test the rest of the circuit after the switch.
If you want to know where to find what sensor does what on your tranny, FSM is your friend.
https://www.nicoclub.com/archives/us...-database.html