I had to guess that you have a 3.1L engine, then I looked at the wiring diagram, and found there are two different twelve volt feed wires to the head light switch. It is not likely both developed a problem at the same time, so we should go back further to the fuse box. Does your car have fog lights, and if so, do they work?
Look for the 20-amp "tail light" fuse. There will be two tiny holes on top for test points. Check for twelve volts on both sides of that fuse. If you find it is missing on both sides, a good suspect is a corroded connection behind the fuse box. GM experimented with aluminum wire around this time period, and it proved to be a disaster. Two different kinds of metal, and an acid, is a battery, and results in corrosion. The rivets connecting the wires to the fuse holders could be steel or brass, and salt is the acid. The biggest problems came from salt on your feet, but water is also bad news. The clue to this is the lights might start working if you push or wiggle on the fuse box.
Let me know what you find.
Monday, January 29th, 2018 AT 5:35 PM