adding extra cigarette lighters

[nitrox6118]

I have a 01 Silverado 2500HD Crewcab with the 3 cigarette lighters in the front. i would like to add an additional lighter in the rear of the cab. i want to splice into the wires for the front lighters and run a wire to the rear of the cab and put one back there. but i am having trouble finding out what to remove to gain access to them. how could i get to those wires?