Wiring Tailight problem
 

I have a 03 h2 and the right side tail light quite along with the side marker. Everything else works on that side, blinkers/brakelights, but no tail light. I took it to a electic guru I know and he said there is a short! HMmmm go figure. Anyway he said I need to trace the wires to where they split off and there should be one wire running back from the front that splits off and go's to each tail light. Any thoughts? Or somone know where these wires might split off? Hate to spend days crawling around under the truck.

Any help appreciated