Just bought an Autometer A/F gauge. WHat wire off the 02 sensor is the signal wire and where is the best spot to tap into this wire? AT the computer harness or just before the sensor

 

The guage will not work 100%.
I have one on my car and it pretty much just sweeps in the rich only. It will light up 2 lights in the middle. It is due to the system in the car. It only reads between .5 to 1 Volt not like the other cars that read from 0 to 1 volt.

What I did was get an O2 harness from a junk car and an O2 sensor plug from a junk car as well and made a pigtail and hooked it online.

Kind of like that plug. I thought I had the actual pick of the harness but I don't. I didn't like the idea if just tapping the wire by the tranny and having it get wet all the time. I sealed everything good and then added the outside sheilding.
Thats the way I would do if it you are still going to put it in.

 

But isn't there just one sensor signal wire? Why does your pig tail have 2 wires? As well are these plugs you made up off of a Volvo or any old junk car?

 

They were from another 850.
Like I stated under the pic that was not the actual harness. That was another one I made for my corner lights and headlights.
Yes there will only be one signal wire.
I cut one side off the engine harness.
I cut the other side off of a bad O2 sensor and thats how I made the harness.