Reverse Light Out - Passenger side only

Trying to resolve this for my Dad. He has a 2003 Automatic. Only his passenger side reverse light is out. I read about possibly replacing the switch on the transmission but don't see anything resembling what's discussed here - https://www.tacomaworld.com/threads/reverse-lights-not-working.510099/

Also weird only the passenger side is out. Anything else I can try?

 

If it is ONLY the passenger side, it's likely the power wire on of the RIGHT tail light.
The power wire gets power from the LEFT taillight.
If you have NO power to the Black/Red wire, then you'll need to pull the LEFT tail light and see if the wires are BOTH in the #5 pin. If so, you need to inspect the wiring TO the right light.

You need to pull the tail light and see if you are getting power to the Red/Black wire.
Power is on pin 5 of the connector. (Red/Black wire)

It not likely to be the ground as the ground for the LEFT is the SAME wire as the Right.

 

Thanks! I will check that out.