Reversing Camera

I am in the process of fitting a reversing camera and could do a little help.
I have sorted most of it out but the video cable has a red wire coming out of it, after research I believe this is called a trigger cable and I believe its function is once you engage reverse using this cable forces the monitor to show the rear view.
My question is where is the best point to wire this cable too?

Thanks a lot  

My best guess id the reversing light .

Yes, use the switched +ve feed to the reversing lights to switch on the signal to the camera

Thanks a lot guys for your replies, but can I just confirm we are all talking about the same wire , as you'll realise I'm not the most tech person in the world!!!!!
What the kit comes (shame it doesnt have instructions) it comes with the camera, it then has a positive and negative lead that plugs into the camera, I sussed this positive lead attaches to the live feed for the reversing light and the neg lead to earth to tell the camera to send the signal.
You also have a lead with a yellow jack plug each end (video lead), this obviously goes into the camera and also the car radio monitor to send the signal from the camera to radion monior . BUT attached to this lead each end by the jack plug is just a red wire, after doing a bit of research I believe this is called a trigger lead and its function is to change the radio from playing music to display the rear view from the camera automatically without manually changing the function on the radio.
Does make any sence at all ???? and can you help please????

Really appreciate your time for replying Guys. Thanks.  
     

A caveat first! I am not familiar with this piece of kit, neither am I familiar with reversing cameras or the radio heads that support them but I have installed regular reverse parking sensors in the past.

Are you sure that the positive lead isn't connected to a 12v feed from the accessory circuit, i.e. a circuit that is 12v live when the ignition is switched to position 1. The red wire on the video lead might then be connected to the 12v feed supplying the reversing lights to indicate that the car is in reverse.

Just a thought...

I'd be asking the supplier - but I guess you've tried that and the english/chinese interface is not working!

Thanks a lot Bruce. You know I've had this kit for a couple of years and never got around to fitting it!! I'll give your suggestion a go. Thank you.

Have a look on ebay and see if you can find the same kit. Often one of the photos is the fitting instructions.

If the cable does need connecting to your head unit you need the instructions for the head unit.

According to the 2003 wiring diagram, the colour of the wire that you need to pick up the switch feed to your camera is the green wire with a brown stripe that goes to the reversing light and can be found on either the right or left hand rear light connector. The -ve ground wire can be grounded to anywhere on the metal frame, or preferably from the earth connection point in the left hand side of the boot, where all the black wires connect to. You could also use the same connections to turn on rear parking sensors. 
The camera will turn on when you put the car in reverse and automatically switch over the screen of the head unit if you are using one to display the image.

Sundance