* Faulty Ignition Switch: This is the most probable cause. The ignition switch is a complex mechanism that controls power to various components. If it's malfunctioning, it might not be properly breaking the circuit to the starter and engine control system when the key is turned to the "off" position. This is especially likely given your mention of needing a "pull switch" - this suggests that a direct power cut is required to stop the engine, bypassing the failing switch.
* Stuck or Malfunctioning Neutral Safety Switch (NSS): In an automatic transmission vehicle like the Intrepid, the NSS prevents the engine from starting unless the transmission is in Park or Neutral. A faulty NSS could remain "closed," as if the transmission were still in drive, constantly sending the signal that the car is ready to run.
* Problems with the Starter Solenoid: While less likely to cause the engine to stay running *after* it's started, a faulty solenoid could be sticking closed, continually supplying power to the starter motor (though this usually manifests as a cranking noise even after the engine starts).
* Wiring Issues: Short circuits or damaged wiring in the ignition system can prevent the proper flow of electricity, leading to this problem. A short could be supplying power to the system even with the key off.
* Engine Control Module (ECM) Problem (Less Likely): While less common, a malfunctioning ECM could be failing to send the correct signal to shut down the engine. This is a less probable cause than the ignition switch issues.
Why the pull switch works: The pull switch acts as a brute-force override, cutting power directly to the engine (probably at the main power relay or fuse), bypassing the faulty component causing the problem.
Recommendation: You should not continue driving the vehicle. The underlying problem is serious and could lead to a fire hazard or other dangerous conditions. Have a qualified mechanic diagnose and repair the faulty ignition system component. Focusing on the ignition switch and neutral safety switch would be the most logical first step. They are relatively easy to access and replace.
