* Faulty Trunk Release Cable: The cable that releases the trunk latch might be frayed, broken, or improperly routed, causing it to accidentally engage when the brake pedal is depressed. This is the most common cause. Movement of the brake pedal may be pulling or bumping the cable enough to trigger it.
* Electrical Short or Malfunction: A short circuit or malfunction in the trunk release's electrical system (if it has one) could be sending a signal to open the trunk when the brake lights are activated. This is less likely but possible. This might involve a corroded connection or damaged wiring near the brake lights.
* Mechanical Linkage Interference: While less likely, some component related to the braking system might be interfering with or inadvertently actuating the trunk release mechanism. This could be due to damage or improper repair.
* Vacuum Leak (if equipped): Some older vehicles use vacuum to operate components. If a vacuum line is malfunctioning or leaking near the brake booster, it's conceivable that it might affect other systems including the trunk release (though this is a long shot).
In short, it's a mechanical or electrical problem that needs to be diagnosed and repaired by a qualified mechanic. Ignoring it could lead to the trunk opening unexpectedly while driving, which is a safety hazard.
