If the fuses are good check the ground. I replaced my ground cable this weekend with one that had a little pig tail on it with a spade. I bolted it to a near by bolt. The lights are brighter and the turn singals are stronger and everthing electrical runs the same at idle or at speed. Don't underestimate the ground.
when you say ground cable, are you referring to the negative battery cable? Just want to clarify because I saw the tailights have ground wires coming off of the back of the bulb fixture. The wires were in good shape and had a solid ground.