* Faulty blower motor resistor: While resistors usually cause *variable* speed issues (like the fan only running on high), a completely failed resistor could short out and provide constant power to the motor.
* Short circuit in the wiring harness: A short in the wiring leading to the blower motor or the blower motor control module could constantly provide power, bypassing the ignition switch. This is a dangerous situation as it could drain your battery and potentially cause a fire.
* Problem with the blower motor control module (BCM): The BCM manages many electrical functions, including the blower motor. A faulty BCM could be sending a constant "on" signal regardless of the key position.
* Ignition switch problem: While less likely given the specificity of only the blower motor being affected, a faulty ignition switch could be failing to completely break the circuit to the blower motor.
* Aftermarket additions: If you've added any aftermarket accessories recently, their wiring might have inadvertently shorted or created a parasitic draw on the system.
What NOT to do:
* Don't keep driving the car: The constant power draw will drain your battery.
* Don't try to fix it yourself unless you have significant electrical experience: Working with car wiring requires careful attention to safety and proper procedures to avoid injury or further damage.
What YOU should do:
1. Disconnect the battery negative terminal immediately: This is crucial to prevent further battery drain and potential fire hazards.
2. Have a qualified mechanic diagnose the problem: They have the tools and expertise to safely and accurately identify the source of the short circuit or faulty component. They can use a multimeter to trace the current flow and pinpoint the issue.
3. Do NOT attempt to run the car again until the problem is fixed.
Ignoring this problem could lead to a dead battery, a fire, or damage to other electrical components. Professional help is strongly recommended.
