Looking at the service manual, you insert the 1.25mm wire into the hole until you "unlock detent of the locking cylinder by overcoming the resilient resistance." Once you've got the wire fully inserted to unlock the detent, then you should be able to unscrew the outer black collar/cap, and once that is loose then you can pull out the entire assembly.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC