I am changing out the lock cylinder on my Bronco. I got the old cylinder out and tried installing the new one, but it does not stay in the switch. I have watched all of the Youtube videos and can't see where I am doing anything wrong, but it isn't working so I must be. Any suggestions?

I ran into the same problem when I installed a new ignition switch a couple of years ago. The problem turned out to be that the slots in the bottom of the new switch were just a hair to small for the tabs on the lock cylinder to slide past them. The fix was filing the slots out a little bit with a small flat file. It took a while because you only have maybe 3/16 " of stroke with the file. Once the tabs would slide past the slots, the cylinder went right in like it's supposed to. Another case of chineeze quality (or lack thereof ).
Mark.

Interestingly, it is the stock switch and neither the replacement lock cylinder nor the original will lock in place. Might be time for a new switch. I don't understand what the mechanism is that causes it to lock in the switch.

At the bottom of the switch there is a landing spot for the cylinder to engage, so something is out of sync between the two pieces.

Thanks, Kinder. That was it. The recess at the very bottom had turn 180 degrees, so I simply turned it till it aligned and it locked first time. Thanks!