Here are the most likely culprits:
* Ignition Switch: The actual ignition switch itself might be faulty. It's possible the switch is sticking or failing to properly disengage when the key is turned to the "off" position. This is the most probable cause given the circumstances.
* Neutral Safety Switch: This switch prevents the truck from starting unless it's in park or neutral. A faulty neutral safety switch might not be properly signaling the ignition system, allowing the engine to run even when the key is removed.
* Wiring Issues: Damaged or shorted wiring in the ignition system could be bypassing the normal "off" function. Look for frayed wires, especially around the ignition switch and steering column.
* Starter Relay/Solenoid: While less likely to keep the truck running *after* starting, a faulty starter relay or solenoid could be contributing to the problem if it's stuck closed.
* Incorrect Installation: Though less likely, it's possible the new tumbler wasn't installed correctly, leading to an unintended electrical connection.
What to do:
1. Check the Neutral Safety Switch: Make sure your truck is in Park or Neutral (whichever your truck needs to start). If it stays running even in Park, the neutral safety switch is a prime suspect.
2. Inspect the Wiring: Carefully examine the wiring harness around the ignition switch and steering column for any damage, fraying, or loose connections.
3. Try a Different Key (if possible): If you have another key, try it to rule out a problem with the new key tumbler itself (though this is less likely given the description).
4. Professional Diagnosis: If you're uncomfortable working with your car's electrical system, take your truck to a qualified mechanic. They have the tools and experience to diagnose the problem accurately and safely. The problem could be something simple, but it's best to have a professional ensure it's safe to drive.
Ignoring this issue is dangerous. A vehicle that won't turn off is a serious safety hazard. Get it checked out as soon as possible.
