Ignition lock cylinder replacement, '93 SL
 

I'm having trouble replacing the ignition lock cylinder on my 1993 SL. I took the old cylinder out with no problem, but can't get the replacement cylinder (or the old one either) to fully seat & lock in place. All the online videos I've seen just say to put the key in the ACC position (so the release button will depress) & insert the cylinder. I do that, but the cylinder stops maybe 1/4" short of fully inserting. What am I missing?? Any ideas??

Not sure, but you might look at them side by side and make sure they're the same length. Maybe a piece of the old one is still in the hole?

Rubehayseed: That was my first thought, but the old & new cylinders appear identical. Also, since I can't get the old one back in either, I'm pretty sure it's something else.

One possible clue: Using needle nose pliers, I tried repositioning the metal piece that sticks out from the ignition switch, thinking maybe it wasn't lining up with the opening in the cylinder. But it doesn't rotate at all. Shouldn't it turn? Or is this indicating that the ignition switch itself is bad?

I would remove the plastic shroud from around the column. Next locate and loosen the screws that hold the electric part of the ignition switch. This part is slotted so the ignition tumbler and the switch can be in perfect alignment. If you have a tilt column the linkage may have flexable pieces involved. This is generic help since I have never worked on an S series column.
To answer one of your questions if you could grab the tab with needlenose pliers. You should be able to operate the electric part of the switch by turning. However the key gives you lots of leverage and the pliers are difficult to hold closed and twist at the same time.