I was removing my header and failed to seperate the male/female terminal to my O2 sensor. As a result it pulled out from god knows where. Any ideas of where I plug it back in to?

 

LOL, the ECU.

Along the harness, I believe it is wired in with the BAC, not sure on a N/A though.

 

So it goes inside of the car?

 

The yellow end of the o2 sensor connector had its wire broken off. Like it was said above look where the BAC connector wires split off from the main harness right around the tstat neck/housing.

 

The dangling part almost looks like the 'core' of an O2 sensor. If this is the connector end, it sure doesn't look like mine (S5 NA)!

 

Yea s5's are different. S5 have this weird black ovalish connector while s4's have the o2 sensor that looks like the knock sensor connector.

 

OK, I just searched that main wiring harness behind the thermostat, and I seen nothing irregular. So that white portion which appears to be broken off, sticks out on the main harness in that area? Can I just run a wire straight to the ECU?

 

Yea you can run a wire straight to the ecu.

 

it's a grey sheathed wire coming from around the T-Stat housing....