where is garbox switch wiring so i can connect stereos gb wire for rear camera on 2004 Volvo S60

need diagram so i can tap into switch wire for reverse back up camera to switch to video mode displaying rear camera when i put car into reverse!

Asked by for the 2004 Volvo S60
just go to the back up lights in the rear of the car for the feed wire for back ups.

thanks and i did that for power to camera but stereo head unit has one wire that needs to be connected to gearbox switch in order for display to switch and show on monitor screen automatically when car is put in reverse so i dont have to manually select camera function.
can you use the same wire for the camera??