So many times with tail lights it is ground issues. Also, replace the bulbs with some new ones. Sometimes a bad bulb can cause some really crazy things to happen, add that to a rat's nest of wiring and it can really make you scratch your head. One more thing... I highly recommend you invest in a couple of books. Get a reprint of the original shop manual as well as a factory assembly manual. The shop manual will help on taking things apart and the assembly manual is really handing on putting things together.
