95-99 Turbo Eclipse/Talon

Undo the driver's right side kick panel (one phillips screw and one plastic push-screw) to access the ECU wiring harnesses behind the center dash. There are four plugs on the ECU. On the UPPER plug (the 22-pin plug), on the top row (the side with the push button to release it from the ECU), there are three white wires in a row. The oxygen sensor signal is the middle of those three white wires. For the record, this is wire 76 on connector number 4. It's the sixth from the left on that plug.

You can use a "vampire" type connector (not ideal), or better, scrape a little insulation from the wire, solder on your air/fuel meter wire, then tape or heat-shrink to cover up your solder. On the other hand, soldering in such close confines is pretty hard, not to mention you're working on your ECU wiring harness, which you do NOT want to damage. So most people use the tap-type connector.