2009 Regular cab head unit w/ factory back up camera

Sorry if this has been asked before but ive searched without finding a solution.

I have a 2009 Tacoma regular cab with the camera already installed in the tail gate. I didn't have the rear view mirror with screen from factory. I just purchased an alpine head unit and would like to hook up the factory installed back up camera.

How do I go about this? Anyone have any idea where the factory wiring ends for this? Any help or feed back is much appreciated.

 

Wire it in