Do you have turn signals in the front? Can you hear the flasher engaging/disengaging when signals are switches?
For my rear lights, I discovered some of the wiring to be chaffed and grounding where the wires go into the light assembly housing. You might want to pull those wires out one at a time and check to see if any metal is exposed in the wire. I also had to turn the wire about 180 degree's for good contact with the bulb.
Have you tried bending some wires at different points along the wire to see if you can get the lights to turn on? Could be a slight break in one of the wires, unseen because of the insulator.