New key lock cylinder replacement problem
 

Howdy. I am attempting to replace the key lock cylinder on my 1999 Blazer with one I got from Rock Auto. The Standard Brand Part is #US287L which should be the correct part. It looks Identical to the cylinder I removed in every respect. It just won't slide completely in as demonstrated in the videos I watched. Also, now the original will not re-install either. The wheels are straight and the steering wheel appears properly oriented based on the Chevy Logo and my recollection of its usual position. It appears the cylinder bottoms out too soon and the base rectangular part does not align with the interior recess by a few degrees. I am at a loss. The videos make this appear to be a no-brainer once the dash is apart.

I am dead-in-the water at this point. HELP!!

Haven't done it, but I think the cylinder needs to be in a certain spot. Try putting the key in and see if you can get lucky.

Key lock cylinder install solution
 

Ok, responding to my own problem with the solution. Maybe, it will help others in the future.

The fix:
With a strong LED flashlight I was able to see that deep into the interior of the cylinder housing was a recess that the lock cylinder had to match up with. By taking a large flat blade screw driver and inserting it in the housing, I was easily able to rotate the component clockwise about 5-8 degrees. This then matched the rectangular part machined into the leading end of the lock cylinder. Then when I inserted the cylinder according to its obvious tabs, it engaged fully into place and locked down. Everything went fine from there. I can't explain how it rotated out of place, as I was trying to be very careful not to disturb anything once the old cylinder was removed.

I might suggest that anyone else attempting to replace the lock cylinder, to perhaps, lubricate the old cylinder with silicone prior to removal. I did struggle a bit while inserting the probe into the release hole in order to depress the locking tab. It seemed to require some jiggling and twisting efforts to get the cylinder out beyond half way.

Again, this problem developed while servicing the Multi-function Switch in order to stop the incessant clicking noise from the relay on the right front passenger side. I was following a pretty good video on cleaning the switch, but it inaccurately stated the vinyl trim piece around the ignition key would simply pry off. It does NOT on a 1999 Blazer, as I found out "the hard way".

Good luck to all those who attempt this fix!