"but quite complicated for an electrical novice like myself"
I'm getting helpful info from a simple DMM. At Harbor Freight they start at $4. That would be enough to monitor mixture (lean burn). I paid more ($33) for a meter with a dwell-angle feature. That lets me monitor how long my injectors are open, which is a direct measure of true, instantaneous fuel consumption.
It's not hard to do. I'd be glad to explain how to do it.
I just looked at the 96 - 98 Civic Helm shop manual. It seems that instead of a test harness to connect to the ECU, back probe pin adapters are used on a standard DMM to connect to the pin outs on the ECU.
Has anyone tried this? It looks like it would work to access D14 and D16.
Each approach has its own advantages. The RS product worked great for me, for this exact purpose (tapping wires near the ECU).
I tapped D14 and D16, to monitor AFR. I also tapped A1, to monitor the injectors (this requires a DMM with dwell, but I found one for only $33). This is very helpful, because it gives me a precise indication of instantaneous fuel use.
I also tapped D18, because my car has no SIL (shift indicator light), and I was curious what it would be like to have one.
There are some other interesting things to tap, but so far I haven't bothered.
I've also become very interested in the possibility of using a cheap ($25-50) data-acquisition interface to display/capture all this data on a laptop, instead of a DMM. I think that creates all sorts of interesting possibilities, greatly exceeding what a Scangauge can do. I wonder if anyone here has any thoughts about this idea.