Where is the back up light switch located on a 91 Toyota 4 runner?

The backup light switch on a 1991 Toyota 4Runner isn't a separate switch like a light switch in your house. Instead, it's integrated into the transmission itself. It's a mechanical switch that activates when the transmission is shifted into reverse. Therefore, there's no separate switch to locate. Troubleshooting backup light issues on this vehicle usually involves checking the switch within the transmission (which requires some mechanical work), wiring, bulbs, or the fuse.