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Most models of cars will have an ignition access hole somewhere around the steering wheel. Check your user's manual to find it on your car. On Fords, there are usually 3 holes under your steering wheel. The smallest hole should be in the middle and is the access hole for your ignition.  On Chevrolet brand cars, the access hole can usually be found on the top of the steering wheel.  New cars that have electronic or push ignitions don’t have lock cylinders. If you don't have an ignition access hole, you'll need to remove the bottom of your steering wheel. Your key needs to be in the ignition or you won’t be able to release the lock cylinder. Keep the key in the ignition as you continue working. Do not turn on the car. You don't have to turn the key initially. As you push the Allen key into the hole, it should disengage the locking mechanism on the lock cylinder. You’ll have to keep the Allen key pressed into the hole as you move onto the next step. The Allen key disengages the locking mechanism in the lock cylinder. You should hear 2 clicks once the ignition disengages. Your car should not start. You can now release the Allen key from the hole. Keep the key in the ignition. The ignition, or lock cylinder, should pop out after you turn it. Pull on the key to pull the lock cylinder completely out of its casing. If the ignition is sticking, wiggle it back and forth until you free it from its hole. Push your new lock cylinder into the hole and twist it towards you. The spring should engage, locking the new cylinder into place. Your new lock cylinder is now installed. You should hear it click when your ignition locks in place.
Find the access hole to your ignition. Put your key in the ignition. Push an Allen key into the hole. Turn the ignition clockwise until it clicks. Pull the key ignition out. Insert the new lock cylinder and turn it counterclockwise until it clicks.