1988 Oldsmobile Ciera Tail lights and other problems

I have an 88 cutlass ciera with about 120000 miles. Recently taillights, instrument panel light, radio, and my running lights went out in a very short period. I did put in an aftermarket cd player into it but have checked the wiring with multiple diagrams and made sure everything was connected good etc. The runnings lights just needed new bulbs. My problem is with the tail lights. I have replaced the bulbs and replaced fuses etc. I also followed the wires through the car expecting to find a bad ground or melted wires etc but was unable to find anything. I am not sure where to go to next to solve this. Any ideas?