The ignition switch on a Chevy TrailBlazer, although generally reliable, may fail suddenly. If it does, you won't be able to start your TrailBlazer. Replacement switches may need to be purchased from the Chevy division of a GM dealership. This is because your TrailBlazer may have a transponder inside the ignition key. If it does, you'll need a new key along with the new ignition switch.
Remove the screws holding the steering column cover in place with a Phillips head screwdriver.
Pull the steering column cover off the steering column.
Put the ignition key into the ignition and turn it to the "II" position.
Push the ignition release button and pull the ignition switch assembly out of the steering column.
Insert the new ignition switch assembly into the steering column where the old ignition switch was located with the new ignition key in the "II" position.
Turn the key to the "off" position and secure the steering column cover to the steering column using the mounting screws.