Need help with Headlight switch

We have a 94 Mazda B 3000 Pickup that we are having an issue with the headlights as well as tail lights. When the headlights are on, no interior or tail lights will work. We can get tail lights and interior lights by fiddling with the headlight switch (which we have replaced twice) but cannot get headlights and tail lights to work at the same time.  No
directional lights work. Fuses appear to be fine. Please help