connections for after market rear view cam

[stephenbb]

Hi,
I installed this camera
https://www.amazon.ca/gp/product/B00...?ie=UTF8&psc=1

and when I first switch to reverse I see the cam working. however when I start backing or just turn the wheel the video disappears and only guide lines remain. I suspect this is sth to do with the electrical. I connect the positive on the camera to plug #4 on the feeder to the back light assembly. for the negative I connect to the feeder for negative on the reverse light bulb. the negative is very interesting here: there are two prongs that slide into a tiny harness and looks like both serve as negative. I can provide pics if people know how to connect the wires.
all videos on youtube skip the wiring, very strange.