Won't shut off

Symptom = starter starts the car but will not turn off until battery cable is diconnected, when the battery is connected again starts without key Request = please if you can tell me what is wrong & give me detailed advise on how to fix it my self Response = Replace the Ignition switch. Assuming this happened before replacing the solenoid and thats why you replaced it. Here is the thing the solenoid sends power to the starter only when it receives a signal from the ignition switch. So you can take a meter to the start wire at the solenoid and see if it has a constant voltage. Un plug the start wire at the solenoid. If there is constant voltage at the start wire on the solenoid replace the ignition switch(NOT the key and tumbler). Now if you disconnect the start wire from the solenoid and it still starts on its own, then you have installed the solenoid or starter improperly and need to check for a crossed wire.