1996 Mercury Station Wagon Headlights won't come on

My headlights high beams & low won't turn on. I recently had to replace the battery, starter & rebuild the power distribution box. Fuses and relays were also checked and replaced as needed. This is when my headlight issue began. I have cheched all wiring & the alternator is not that old. Could my problem possibly be in the dimmer switch if not could you give me some ideas.