Reverse lights

So I have an 05 toyota corolla and I bought an aftermarket stereo. To hook it up I had to scour the internet trying to find the factory wire colors to hook it up... I now have to hook up a reverse cam. I have everything hooked up and ready to go concerning the cam. I now have to run a wire to the positive reverse light wire in the trunk. I dont know which is the positive and which is negative. If anyone knows anything out there.. please enlighten me