How do you fix the tail lights to a 1968 volkswagen beetle?

Use a test light (any auto parts store) and check to see if you have power at the light socket. (Make sure the test light is grounded good by checking a known good light). If you do then try to clean the oxidation off the contacts on the bulb and the socket, with the power OFF. Also make sure you have a good ground for the tail light housing. I had that problem too. There should be a ground wire from the fender to the housing and from the housing to the light socket somewhere in there. If your fuse is good then check the power there too as the contacts for the fuse in the panel will corrode also. You should buy the Bently manual.