Paul, my BMW 3 series E46 rear lights are constantly on. I have to disconnect the battery terminal to avoid running it down. What could be the cause? Haguma
Hello Haguma, you will need a computer diagnosis of the lights module to confirm whether the brake lights have a short circuit or the brake switch under the brake pedal has failed.
In the absence of computer diagnosis, I would start by checking the brake switch. A qualified car electrician will inspect the brake switch for damage of the spring return mechanism or contact plates.
Should it be fine then proceed to inspect the brake light circuit. The trouble caused should be found quickly.