Toyota Repair: 1990 Brake Light bulb, toyota 4runner, broken wires

Question
I have 1990 Toyota 4runner.  I have a problem with the brake lights. When the headlights are off they work fine (go off when you’re not applying the brakes and light up when you are applying the brakes) but when the headlights are on they don’t. When they are on the brake lights are always lit up and never get brighter when you hit the brakes or when you let off the brakes they stay the same brightness/ they don’t dim when your not on the brakes they are always on. We checked the bulbs in the truck and they are the right ones. What could be causing this problem? Thanks  

Answer
Check the wire harness on the left trunk hinge, the wires inside the harness can break and short out, open the harness and check for broken wires all the way into the passenger comparment, another reason may be the lamp failure relay, it's located in the trunk on the left behind the carpeting in the fender, it's attached to a metal bracket.