Back night time tail lights on both sides won't come on

Check your bulbs first. Then check the sockets for corrosion.

Turn on the light switch selector. I see multiple cars every day driving around with no taillights and they are completely oblivious because Thier daytime running lights appear to them as headlights.

There are a number of possibilities depending on what vehicle, the age of the vehicle, engine on or off, the status of the lights in all the different switch positions.
Do license plate lamps come on?
Do you have trailer electrics? If so do they work?

Vehicle information needed and specific problems .

Check fuses, if fuses are good then verify the bulbs are good. Check power supply to the taillights. It could be the bulbs, a fuse, the fixture, or the headlight/tailight switch. It's pretty unusual to have damaged wiring unless a rodent got to it or there is high resistance.

On what? What are you talking about?