All good advice from 68 topless. The only thing I would add if you have little experience is to always start simple. First check easy things like bulbs and when removing from the sockets check for corrosion inside the sockets because the socket to the metal side of the bulb is part of the grounding circuit. If corroded clean down to bare metal with emery cloth. When testing for electrical faults you need either a multi meter or at least a test light. Clip the black negative side to a known good ground, double check this step. Then take the positive probe and test the socket wire lead while the blinker is on and you should see the power blink on and off, if you do and your bulb is ok then you have a grounding problem And don't forget what 68 topless said, in the front the housing is screwed into the sheet metal for ground and in the rear the sockets get ground from the spring loaded clips that hold the sockets in the tail light housing. after cleaning all your connections put a little electrical dielectric grease to help the connections and to keep them from corroding again.