1989 Dodge Dakota O2 sensor

I had a friend replace the TBI injectors and he noticed the wire on the o2 sensor on the exhaust was broke after the connector. He couldn't trace the wire. Do you know where the o2 sensor connects or its destination or the color of the wire. I imagine it goes to the control mod on the fender well? He said it was a single wire sensor. I haven't seen a single wire sensor before. The truck runs better with the new injectors but the o2 sensor is nessesary for proper fuel mix. Any help would be appreciated. Thanks, sam.

1989 3.9 tbi