RE: Air/Fuel Gauge
with the car running, strip back a piece of each of the wires. Use a multimeter. One wire will have 0 volts (ground), one wire will have +12 volts (power) and the other wire will fluctuate, but will remain between 0 and 1 volt. Hook up to the wire that is betwen 0 and 1 volt.
Keep in mind, that your air fuel gauge will not be very accurate. A typical oxygen sensor can't tell you what the air/fuel ratio is with any degree of precision, all it can really tell you is whether the car is running lean or rich.