Reverse wire for AVIC X920bt
So, I got a backup camera for my truck and was trying to install it tonight and got stuck when I tried to wire it up to my head unit. The problem I am having is figuring out what wire coming out of the head unit is the wire that triggers it to turn onto the camera when I shift into reverse. When it was installed, they removed the tag (if it had one) that told which was the reverse wire. Every search on google I try always tells what wire it needs to get hooked up to, not what wire it is. The only place I did see mention of a wire coming from the head unit was a violet and white wire, which mine doesn't have... Please help!