Can I tie into the backside of the ECU plug in order to pick up information?

I want to wire an air/fuel ratio meter that reads the signal coming from the O2 sensor. It also has a % open on the injectors as well. Both of these need to come from the ECU wiring harness. Both are just plugging a wire into the backside of the ECU harness.

I'm not changing anything with this wiring, just picking up information as part of data collection. The rule states that the wiring harness to the ECU must be un-altered, but we're allowed any kind of data collection & instrumentation. Could be useful for data logging.

Thanks
Matt