The reverse light switch is on the passenger side of the transmission.
Now your wiring very well could be totally different colors and positions especially with my IK-2 connector which I couldn't find a wiring diagram for. My vehicles were 2000 Tacoma and 91 4runner for reference. On mine the B-O wire is power to IK2-16 which matches up to switched power IH2-8 also B-O but it says its B-BR.
The signal or return power wire on my harness goes to IK2-2 which is R-B at the harness but at the transmission I think it was a different color. That went to IH2-7 R-W.
Here is the transmission location.
And to test the switch put your ohm meter on the two contacts and depress the ball on the switch. And this can be done in or out of the vehicle with switching between reverse and neutral.
Hope that helps.