Start at the bulb sockets and see if you have power, if not check the fuse. If the fuse is good then find the harness connector that goes to the back of the truck. Check to see if you have power there, if not, keep chasing the wires forward until you find power, and the loss of power will be between there and the next connector where you didn't have power.
If you have power to the bulb sockets, then you must have bad bulbs. Make sure that you have installed the proper bulbs. Today there are more styles than just 1156 & 1157. The wires are in different places on the different variations so the correct part number is crucial.
