I have a 2005 Silverado I just put a ls3 in it. I got the tac to work. But my question is about the oil pressure sensor. The ls3 is ...

I have a 2005 Silverado I just put a ls3 in it. I got the tac to work. But my question is about the oil pressure sensor. The ls3 is a stand alone system. My question is does the ecu need the grey wire from the oil sensor to go to the ecu. It currently is but in order to get my oil gauge to work I need to come from the sending unit directly to the cluster. People keep saying it’s a tan stripped wire going to the back of my cluster. But that wire isn’t there. Would you know what pin it’s suppose to be in so I can add it. Also how does the cluster get the signal to it