Key switch cylinder won't slide in!

Hi, I got a 1981 stepside Midnight Express pick-up clone.
I bought a new key switch cylinder, but it won't slide into the steering column. Besides the normal tiny peg that locks it in place, there is also a sharp prong sticking out which is preventing the installation! The old cylinder has it too, but it is folded down inside the cylinder.
No matter what I've tried on the new cylinder, the prong won't fold down! Any ideas?????

I'm assuming you have worked w the key every which way & it will not fold flush? & the nub does not move it's just a locking nub right?

Yes I did with the key, but it won't budge. The column has the lever for key removal oafter the engine is turned off.

Just figured it out! It went down when I pulled the key out! Ooops!!!!!!!!!!! Thanx!

I hate to say it's defective as I do not know that system but something that simple there's nothing else to do to get it to lay flush that I can see but we might be missing the "secret". It does seen unfathomable that a simple new part such as a lock cylinder is defective and we're not talking about the more complicated tumblers on the inside just a locking catch

Well, the missing secret was to remove the key, and it slid right in and works fine! Ulimately it isn't the first time that I felt stupid in my life! My autobiography will contain many chapters worth of my stupidity!...and a few pages on my triumphs!!! If anyone wants to tell one of their stupid moments, feel free to do it now and draw the attention away from me!!!!!!!!

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If anyone wants to tell one of their stupid moments, feel free to do it now and draw the attention away from me!!!!!!!!

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Always ready to help my fellow man. I rented a house from my shop buddy and right off the batt I called him to send the HVAC guy over as my thermostat was not kicking the furnace on & I was freezin . I was gone when he sent the guy over & later he called me & said in addition to turning the temp dial to where you want it you also have to flip the little lever over from off to heat . Forgot what the trip charge was he was billed but he (my buddy) let it slide but I was razzed over that on (regular) occaision for months whenever something came up in conversation about my competence/decision making abilities