I got an afr gauge as well to install on my mother in laws wrx. I hooked up the signal wire to the white wire on the rear o2 sensor. I wasn't sure if this was the correct connection because the only reading I got was very faint. It was the furthest red on the lean side, and hardly showed up at all.
I got the information off of this site (for the white wire hookup) and I just wanted to come back and make sure I did this correctly. (Figured I'd just add on to this thread)
Anyone else make this hookup differently. Thanks in advance.