cargo light

I have installed a camper shell on my 2004 silverado ext cab, and I would to tap into the rear cargo light. I could just push the cargo light switch on the dash and the light would go on inside the shell. I would like to tap into this wire somewhere down by the seats. I can only assume that this wire runs along (under) the wire trough under the driver door. Could someone supply the color code of this wire? Thanks