okay, heres the problem. When i brake both taillights work good. When i have the headlights on, then brake, one side works, the other doesnt. What is wrong? Please help me with this.

 

Ok,...I dont know if this is going to help but maybe it will be a starting point. One day I hit some railroad tracks at a high rate of speed and when I came down very hard by the way I noticed that my blinkers and headlights were out of wack. After some playin around I found that on the inside of my blinker switch on the steering column that an electrical contact was thrown out of place. I flipped it over to the right postion and everything went back to normal. But anyways, start by checking for blown fuses. And does this happen with the same tail light 100% of the time?

 

Could be a bad bulb too, those bulbs have dual filimants, some of them anyway, and maybe one of them is corroded or something of the like. Get back there and look at em, pull em out check for broken wiring, bad connections.

Sounds funny if they are getting power when the lights are off and acting strange when they are on.
It could be something else, but thats where I would start. Bulbs are like 2 bucks, replacing them cant hurt.

 

+1 on bad bulb. Thats most likely what it is. I had the same prolblem before just had to replace the bulb.