[Tommy]

I'm assuming a lot about your car, but here goes. Each tail light assembly probably has two wires coming from the rear of the light bulb part of the assembly. There is likely a third wire from one of the bolts holding the assembly in place to a nearby ground. First, make sure each assembly is in fact grounded. Of the two wires going to the back of the bulb, one goes to a bright filament and the other goes to a dimmer filament. When you step on the brakes, only the bright filaments should illuminate. If one side is bright and the other side is dimmer, that may be part of the problem. When you turn on a turn signal, the bright filament on that side should flash on and off. If your turn signal circuit is wired correctly, that will happen whether or not you are stepping on the brakes.

If both assemblies are grounded, and both bright filaments light when you step on the brake, and both dim filaments light when you turn on the parking lights, then your tail lights are likely wired correctly. If this is the case, the problem is likely under the dash where the lights are wired to the various switches. Do a little more troubleshooting and tell us what you find out.