O2 sensor wiring + signal ?

[B318M42W]

I replaced my old O2 sensor with a wideband LC-1 and wired in the simulated narrowband to the original black sensor wire. no CEL light until the engine's fully warmed up and then i get the CEL. I'm pretty sure it has something to do with the other wire (the yellow one, ECU #71). my question is: what's the use of that wire??? do i just ground it to get rid of the CEL?
thanks!