Signal wire on Oxygen sensor???

[cali yaris]

Rear sensor is not heated pretty sure, and not useful at all for air/fuel.

For the front sensor:

I pointed someone else to the wires and where to connect them, but his AFR gauge couldn't handle the offset voltage. Most gauges seem to want to be connected to their own sensor and not share the sensor with another device.

It's best to add a dedicated bung for an air/fuel gauge IF that's what you want and IF you want it to be accurate.