1990 Chevy S-10 Lights

I discovered that I have no tail lights or side marker lights. The brake and turn signals work. I checked the fuses and they are good. There is power going to the bulbs so I replaced one bulb to see if it worked and it didn't. The kid that owned the truck had a toggle switch for a subwoofer and when the truck was sold he took out the switch. The switch was located above the headlight/parking/dimmer switch. I looked behind the switch and it does not appear that he spliced into the wires. After I looked at the wires I turned on the parking lights and the tail lights worked and the drivers side marker and the right hand turn signal stays on in the dashboard and that is the tail light I replaced. Now if I turn on the head lights they all go out I am back to just having brake lights, headlights and turn signals. Any suggestions???