I got pulled over by a cop once because my tail lights were out. I had recently been working on the wiring so I was fairly positive where the problem was. I realized, on the side of the road, that it was indeed under the dash. Turns out it was in the headlight switch. I don't remember if that circuit came unplugged or if I just had one of the circuits wired backwards or what, but that is where the problem was. Hope that helps.
JACK