bad connection/short or burnt out brake bulb. Check the harness both under the steering wheel and at the lights.
You have blown a fuse, look for an acc. fuse out.
The only way your headlights can come on when you press on the brake pedal is a crossed wire. The brake light wire and the headlight wire can be frayed and touching each other.
If it's like a 1996 tracker the headlights won't come on unless the parking brake is released or the light switch is on.
Brake lights should NOT be effected by the headlights. Brake light function is completely independent of the headlights. Assuming you are not refering to the tail lights, or marker lights, which are supposed to come when the head lights are turned on. Not having brake lights when the head lights are on is a big safety problem and should be corrected.
Break lights come on when you step on the break, they do not come on when the head lights are turned on.
Check that your hand brake is all the way down. If your hand brake switch is tripped, the brake lihgt should come on, and the automatic running lights won't.
my 05 Chevy impala brake light come on when my vehicle is turned off killing my battery.
The brake lights should not come one until you step on the brakes. The tail lights should come on when the headlights are on. If they're weak, maybe there's dirt in/on the lenses or maybe the bulb is old and clouded. Change the bulbs and see if that improves things.
Possible ground issue at the taillights.
Press the parking brake down one click. Unfortunately, this will probably cause your brake warning light to come on.
if parking brake is on, the headlights when first started, will not work until brake is released.
Please check that the brake light bulbs are installed correctly and that they are not back feeding the side lights