I'm not entirely sure what tail light bulbs Tacomas use, but make sure that the correct bulbs are in the holders. I had bought a Corrado years ago that had the same problem, except that the parking lights would also come on when stepping on the brake. The problem was that the previous owner had replaced the taillight bulbs, which needed 1157's (dual filament), with 1156's (single filament). What was happening was that when I stepped on the brake pedal, that allowed power to be fed into the park light/dash light circuit. I had spent two weeks trying to track down what I had figured was a massive short before I found the problem.