Hello. I'm trying to figure out my tail light problem. Everything's working. Except the tail lights? I've checked the dark brown wire which to my knowledge is suppose to be the tail lights. At the control switch on the dash. And it don't light up. So I'm not sure if it is the tail light or not? I have a 96' 3500. With a bush box. If I can get some pointers on where to look now. That'd be great.