Symptoms of a Bad Ignition Switchby TJ HintonUpdated August 01, 2023
Key-type ignition switches use a keyed lock cylinder to control the position and function of the switch. Normal tumbler wear and the accumulation of dust and detritus in the cylinder can cause the switch to be resistant to turning, and could exclude or trap the key. This will usually be preceded by increased effort at the key. Switches that are mounted separately from the key cylinder, such as in automobiles, can suddenly cease to function with a concurrent lack of resistance at the key. This is usually caused by a failure in the linkage connecting the key cylinder mechanism to the actual switch located farther down the steering column. Switches that are integrated with the key cylinder, such as on motorcycles, boats, off-road vehicles and older cars, may work intermittently based on position and pressure on the key. Sometimes, wiggling the key sideways or pushing it in while turning it can override the symptom. In cases like this, the terminals could be corroded or loose, or it could be that the contacts within the switch are bad, and the switch needs to be be replaced.
Intermittent complete failure of the systems powered through the ignition switch is the main symptom of a bad switch. Sometimes this can manifest itself through only the starter circuit, with the accessories circuit still providing power to the lights, etc. However, the accessories circuit may also fail in the switch, preventing the operation of any devices. Loose terminals at the switch can cause arcing, which may be audible as a slight tick, and could be accompanied by the smell of ozone or burnt insulation. This will also cause amperage spikes in the affected circuits that can affect your circuit protection.
Before troubleshooting your ignition switch, check all fuses and fusible links related to the accessory, main and starter circuits to eliminate a simple and common cause early. Make sure that your battery is showing around 12.5 volts. If you are working on a vehicle with an integrated cylinder and switch that are subjected to the elements, check the terminals for looseness and corrosion. You may need to remove the terminals and crimp new ones on if you find corrosion or damage from arcing. Check any other connections involved, including the battery terminals and chassis ground strap.
Besides the inconvenience posed by being stranded, a bad ignition switch can cause more immediate threats. If the switch should suddenly interrupt power to the ignition circuit while driving, you will lose all power and power assist to your controls. Switches with loose or corroded terminals can build up heat, possibly causing an electrical fire. If the starter circuit in the switch goes bad, it can potentially cause a runaway starter when actuated. This can cause the starter leads and starter motor to overheat and burn, and the heavy discharge can also damage your battery.
TJ Hinton trained as an auto mechanic at Mississippi Gulf Coast Community College and then later graduated from MMI as a certified motorcycle mechanic . He's also worked for 20+ years in home construction, remodeling and repair. His articles appear on InternetAutoGuide.com and TopSpeed.com.