ok so i got a air fuel ratio gauge today and i am about to put that sucker in...just wondering if i can some how tap into the o2 sensor harness somewhere under the hood....and if not what o2 sensor should i tap??

my car is a 1996 A4 2.8 12v

 

On past cars, I had a three-wire setup. One was power, one was ground, and the shielded, thicker-diameter wire was the signal wire. Just tap it on the O2 sensor side of the connector (not the car side). I can't tell you for sure which wire it is - unfortunately my book is at a friend's house, but I'm sure someone will chime in.

 

i wired mine into the ecu. there is a grommet hole already there.

here was a writeup that i used on my install. it was also a 12v

The ECU box is located on the driver's side under the hood. It is a black box directly under the windshield. You can't miss it. There are 4 or 5 screws you have to remove to get the cover off than there is a metal band to pry up which holds the ECU down.

Here is a pic of the harness that contains the O2 sensor leads. There is 3 solid light green wires in the harness. (Ignore the striped one.) One is very slightly different than the other two. I could BARELY tell. The other two light green wires are your O2 sensor leads. Tap either one. Get some of those T-taps, they are great! Don't worry about tapping the wrong light green wire. You'll know when the gauge doesn't work. I have heard someone say their harness didn't exactly match mine and UrS4's, which is wierd. You'll just have to dig in there and see what you come up with. You do need to peel back the black cloth tape around the wires to access them. Good luck and let us know if you have any questions!

http://pictureposter.audiworld.com/67348/dscf0766.jpg