I peaked into the
DLG-1 Documentation / Manual before buying this thing (again cause it was so darn expensive that I spent nearly 2 years window shoppin', ha ha) and
I was more confused than a goat on astroturf
cause you can see for yourself in the diagram below that this gauge only has one SENSOR CABLE CONNECTOR (the other wires are for something else, the Red/Black/Yellow/White are for hard wiring it for ground and power and the dim switch, standard stuff, the Serial In & Out that's something else entirely, more on that later, but it sure aint for the second O2 sensor)
now you may think geez man why you making a big deal out of this, obviously it works some how, well I think it is important to conceptualize this as it will help you / us when we build up their entire Diagnostic System, you just wait and see, follow along for now, please