If it works when the lights are off but not when they're on, you probably have a grounding problem. Make sure the ground wire of the bulb is connected solidly to the vehicle frame. Also verify that the connectors are not corroded.
check your parking light grounds,lights are trying to ground back thru the circut .common to lose ground in the light socket or even a shorted bulb. most part stores have replacement sockets
This will happen if the ground terminal for the brakelight bulb is connected to the power side by accident. If you have a 3 wire socket or light assembly with GROUND, TAIL, and BRAKE wires two of them are wired incorrectly. When the headlights are off the brake light is finding ground thru the filaments of the headlights. Since the headlights have much heavier filaments, they provide a good ground for weaker brake light. When power is on the headlights the brake light will have power on both sides, so no current flows and it goes out.
The brake lights and the tail lights are separate circuits. Check the brake light fuse, then check the brake light bulbs, then check the brake light switch.
the light doesnt go through the fog
Check the bulbs one of the 2 filaments may be burned out
WHAT ARE YOU DUMB REPALCE YOUR LIGHT BULBS STUPID! Not stupid replaced circuit boards checked fuses ran test light . When headlights are on no brake light or taillights and have all new bulbs stupid. Turn headlights off brake lights work, so figure that out smart man
check brake light switch
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.
The brake light switch can be found below the dashboard on the drivers side of the passenger compartment. The brake light switch simply plugs in and out.
The ground for the brake lamp. When the tail lights are off, the tail light circuit can act as a ground for the brake light. When the tail lights are on, it can't.
You can only turn off the headlights by applying the emergency brake. When the emergency brake is on, the headlights will not light. Otherwise the best of my expererience is that they are on all the time. If you have remote start, put the emergency brake on before you leave the vehicle and when you remote start it, the headlights will not be on, but the driving lights (if switch is on) will be on as well as the parking lights.
You have blown a fuse, look for an acc. fuse out.