voltage regulator problem

well the next chapter in my resto saga. Was getting ready to mount the regulator and noticed I have 2 of them in my pile here. I have a 2 prong and a 5 prong. I look at the plug on the car and it is a 5 prong. some of the wiring diagrams I have show a 2 prong. One wire to the alt. and one wire to the ballast resistor. My question is why do I have a 5 prong on the car. what is the difference and do I use the 2 prong or can I use the 5 prong. confused here. HEEEEELLLLLLLLLLLPPPPPPPPPPPPPPP.