The ones I have seen just have 2 wires. connect them to 12vdc to operate one way and reverse the polarity to operate the other.
from your other post it sounds like the polarity is not getting reversed. you can check it with a volt meter or just reverse the wires at the actuator and if it moves one time then thats the problem. I dont know if the relay that you replaced is what acctually reverses the polarity it might be done some where else. Here is a web site that somewhat explains a actuator.
http://auto.howstuffworks.com/power-door-lock3.htm