ID for Guage Cluster Wire
 

I have a '92 190e that i just put a heater core into. And its almost all back together. I managed to keep track of all the wires, no issues.... except one. The long black male single-pin wire coming out of the cluster. I can't find where that goes. The only spot it fits is a back into the cluster, but a similar wire coming out of the dash goes there. Where does this go?