why use the factory o2 sensor, get a wideband o2 sensor and have it dedicated to the gauge reading only. that way you dont run the risk of throwing the PCM off when you tap into it. most of the air/fuel gauges when you tap in to the factory one will just bounce back and forth as the o2 sensor crosscounts
I have the same Auto Meter Air/Fuel ratio gauge already installed on my 04. If your looking at PCM while it's still plugged in your going to want the connector that's closer to the fire wall. For the up stream O2 signal you want the all white wire, but be careful there are two solid white wires. The other goes for the throttle postion sensor signal. Pin 30 is the O2 signal wire if you can tell what pin that is. If nothing else just test the wire from the gauge with the car running, if it's the right one it will switch back and forth. I've had mine hooked up since week one and have had no issue with it, I recommend not cutting the wire but taking enough insulation off to wrap the gauge wire into wire for the PCM. Just so there is not any resistance issues for the PCM. Other than that just tape it up excessivly and run the wires clean, let me know if I can be of any more help.