speedometer

I have a 85 iroc it has a 350 from a 88 vette, and the transmission is a 700r4. the question is the speedometer cable that comes out of the transmission to the engine compartment, Then there is a cable that comes out of the back of the dash panel through the fire wall that comes from the speedometer gauge. I need to know whats in the middle of the two cables to make them hook together, So the speedometer will work. If any one has a picture or know of a web site that i could go too. I don't need anymore speeding tickets:nono: