Problem with Jeep Grand Cherokee brake/tail lights

During the day the brake lights work fine. When I turn on the headlights the tail lights are very dim and then when I hit the brake pedal the tail lights go off completely and there are no brake lights or tail lights at all. Another odd thing is, the brake light located on the top of the hatch back is always on when the headlights are on. Any suggestions? Sounds like a bad ground to me. Also, if you have trailer light wiring installed, check that also. I have had many problems with them in the past. Your cherokee might be positive grounding, so check a repair manual. Hi:

One simple thing which you can do is check the tail light bulbs. Light bulbs have a tendency to short out (actual filament inside the bulb), Car Repair Talk's forum.