OBD 0, O2 sensor help. Need to know the location of the o2 wire from the harness

[Om3ga]

This is a 88-91 si a6. Too many people have had their hands under this hood. I have accountability for everything but the o2 sensor wire. I cannot find it. I do have a black wire coming out of the harness underneath the distributor, but it is a shielded wire with another wire inside of it. Is this the wire thats supposed to be going to the o2?
Thanks

 

[RonJ]

The stock O2 sensor wire is white and pins to ECU C16.

 

[Om3ga]

Thanks for the info. I know the pin out. Just need to know where it comes out of the harness.

 

[RonJ]

C157 = O2 sensor plug