I've got a '79, so I have no idea if the switches are the same, but for me the problem was with the headlight switch itself. I took apart the dash and discovered that the headlight switch is separated into two main sections, and the front had somehow become almost disconected from the back piece. The result was almost no electrical contact, and hence no headlights. The parking lights and blinkers still worked though. I just glued it back together and it's been fine since. I hope this helps, and if it sounds confusing, it will be really obvious when you take a look at the switch itself.