Mazda,Adding cruise control on a factory non equipped car.

I have a 2010 mazda3 I sport. My car did not come with cruise control. I went the junkyard and got the controls for cruise and installed them. My brakelight switch has 4 wires going to it wich signifies it is 4 pronged. I read from oreilys that a 4 prong has cruise control abilities. I also performed a Guage self diagnostic and it showed a cruise control light. So, I have the light, the switches, and I think, the right brakelight switch. The dealer wants to charge me $110 to "see" if my ecm has cruise control capabilities and to turn it on if it does. I talked to a couple of differe