sports cluster

I recently bought a sports cluster (the one with the tachometer) to put in my VC commodore L. I have all the wires and every thing is working just not the tachometer is there a special plug that goes on the back? or am I missing wires that go on the back of the tachometer itself? Also the oil...

I bought a sports cluster for my commodore L model and the wires to make the rev counter work are not there. The temp gauge, volt gauge, speedo, and fuel gauge work. Does anyone know how to get the rev counter work? Is there more wires or should it just work?