How do you replace an ignition key cylinder on a GMC?

You have to remove the steering wheel and the turn signal switch. but move to the side. It should be empty. There should be a screw where the cylinder is. Just unscrew that and the cylinder should slide out. And make sure not to push the shaft where the steering wheel attaches too. Its a pain to get if you push it in.
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There are other concerns....you probably have an airbag in the steering wheel. You MUST disconnect the battery for at least 15 minutes to power down the airbag or it can go off. I usually wait 30 minutes.
You will need a special tool to compress the steering wheel lock plate to remove the snap ring.
You will need a steering wheel puller. Also a Torx drive bit to remove the key cylinder pin/bolt combo.
Just take your time and pay close attention where all the parts go. I wish i could be there to help.. I've done a TON of GM steering columns.
One last thing...NEVER have someone in the drivers seat when you re-connect the battery. If the air bag is going to blow that is the time that it will go.
Best of luck...

Yeah I didnt think of that. Was thinking of an older model truck. Thanks other dude for your input.