Somebody?

The plug is yellow in color and connects to another yellow mount that has two copper posts in its center. The wires of the yellow plug are covered on its length with a black protector, which is wrapped with yellow tape and follows to the steering wheel and then to a box behind the radio. There are four holes on the plug. There are the two square outer holes and in the center there are two rectangular holes. Which are the correct holes to insert the jumper wires?

I am not getting any voltage readings at the plug with the ignition on.

Does anyone know what the voltage should be?