Hey guys,
Sorry for the delay in responding to some of your questions, but it was a busy work week.
First I ran the wiring along the inner wheel well and secured it so it wouldn't get snagged on anything. You can see how big the harness connector is. I also wrapped it to keep dirt and grime out.
Sal had suggested running the wiring from the O2 sensor through the large grommet in the LH rear seat footwell area, which you can see part of in the lower right of the next photo. I initially tried that but decided to find another solution because the connector that goes into the back of the gauge is rectangular and has small tabs on the ends, so I was concerned about possibly breaking it while trying to force it through what is already a tight grommet. And because I was worried about the cable not being long enough, I wanted to run the wiring up the center of the car and not on the LH close to the door jamb like Sal did because my gauge is closer to the center of the car. So I drilled another hole and then added a grommet and silicone sealer:
Then I ran the wiring through the LH inner seat rail and up to the pedal cluster. Because I have removed the A/C, I was able to run the wiring through an existing hole in underneath the dash into the smuggler's box and then out to the back of the dash in the frunk. (Please excuse my loose under dash wiring. I've removed a lot of interior components, like the center console and original dash, but am trying to keep most of the wiring for the time being.)
After test driving the car, I agree with Dick that the value of an AFR gauge is seriously diminished without a data logger. The nice thing about the AEM gauges is both the voltmeter and AFR gauge have wires in the harnesses that can be connected to a data logger. Mine are not being used now, but I expect that'll change in the future.