* Ignition Switch: This is the most common cause. The switch itself is worn or faulty, allowing power to the ignition system in the "Run" position. It's failing to properly break the circuit when the key is in the "Run" position.
* Neutral Safety Switch (if automatic): If your Mustang has an automatic transmission, the neutral safety switch prevents the car from starting unless the transmission is in Park or Neutral. A faulty switch could be bypassing this safety feature, allowing the starter to engage in the "Run" position.
* Starter Solenoid: A sticking or faulty starter solenoid could be constantly energized, causing the starter to engage even without the ignition switch fully activating the starting circuit.
* Wiring Issues: Damaged, corroded, or shorted wires in the ignition system could be creating a short circuit, bypassing the need for the key to be in the "Start" position.
What to do:
It's strongly recommended you do not continue to drive the car in this condition. Driving it with the starter constantly engaged could severely damage the starter motor, battery, and other components. The starter motor is not designed for continuous operation.
You should have a qualified mechanic diagnose and repair the problem. While some troubleshooting can be done at home (checking wiring, cleaning connections), the internal components of the ignition switch and starter solenoid often require professional attention. Improper repairs could lead to more significant issues.
