There are a variety of different ignition cylinder designs for vehicles, some of which require the original key to turn the lock cylinder to the accessories position to fix the part in the most efficient way. However, if you do not have the original key, then you will need to replace the entire ignition switch assembly rather than only replacing the lock cylinder. Due to the complexity of automobile keys, it is much more difficult to pick the lock cylinder of a car than picking one from a standard doorknob.
Disconnect the negative battery cable from your vehicle, which will eliminate the chance of getting shocked while working on your ignition switch assembly. If your vehicle has an airbag, disable it by prying off the airbag switch cover on the bottom or side of the steering wheel and disconnecting the electrical connection leading to the airbag itself. Wait for 10 minutes for any built-up charges to dissipate from your car's electrical wiring.
Use a screwdriver and socket wrench set to disassemble the steering column covering and lower dashboard panels so that you can access the ignition switch. Different vehicles will have varying panel combinations that need to be removed, however, you will need to see the complete steering column and ignition switch assembly.
Disconnect the electrical connection leading to the ignition switch. Some vehicles may have two connections that need to be unclipped.
Use a screwdriver or socket wrench to unscrew the mounting bolts (or screws) for the ignition switch. Unbolt the ignition switch housing and assembly, which contains the lock cylinder. Some models have interchangeable lock cylinders that can be removed by turning the ignition key to the accessories position and inserting a pin into a pin hole with a release mechanism. However, other vehicles do not give you this option.
Inspect the mounting bolts for your ignition switch housing. Some models use safety snap-off bolt heads that prevent thieves from replacing your ignition switch and driving off. You will need a power-drill with screw extractors to drill out the bolts used to mount the ignition switch housing to the steering column.
Replace the ignition switch and lock cylinder assemblies. Some models may require you to insert the lock cylinder into the ignition switch assembly if the two components are sold separately. This is best done prior to installing the new components to your steering column. You may need to turn the new ignition key in the lock cylinder to the accessories position before inserting it into the ignition switch.
Test your ignition switch by reconnecting the electrical connections and the negative battery terminal cable. Turn on your vehicle. If it cranks correctly, then all you need to do is reconnect the airbag and steering column covers and panels.