Thoughts on Electrical Problem

So as we are putting my car back together, we suddenly developed a small electrical problem. Having put the dash back in the car and reconnected all of the electrical systems under the hood, everything seemed to be working fine. All of a sudden, the rear lights and rear turn signals stopped working. All of the fuses are good. The electrics in the dash seem to be fine and the forward (underhood) electrical system seems to be working as well. I would appreciate any thoughts as to what might be the cause of the rear light failure.