A "real" AF guage doesnt connect to your O2 sensor.
The 02 sensor in your car wont give you a correct or even CLOSE A/F reading when you connect it to a stock "narrow band" sensor.
If you want to do this, and do it correctly you need to have a seperate Wide Band 02 sensor added to your exhaust.
Just say no to putting a gauge on a narrow band sensor, that is RICER MODS.