Which Line to tap A/F Gauge line to on sensor

[DatSRBoi]

I had my A/f Gauge sitting in my car for awhile now and Finally got time to hook it up today. I got the positive line in and negative...But not sure where to tap the last line...Too lazy to have to find it...So..

I know and was told to tap that sensor near the converter on the exahust pipe on the bottom of the car..I see theres a sensor there so Im guessing thats the A/F senor...Can anyone tell me which line Im suppose to tap into? Or where is that sensor that Im recommended to tap in.

I post in this forum since its the only boost people put a/f gauges in their car... Or....Most..