300D Transmission Issues

Pursuant to a number of earlier posts, I have managed to free the kick-
down button switch on the firewall of my 300D and believe that it can
now be removed without breakage. I have not yet done so. However,
would someone please explain in detail how this is supposed to remedy
the problem of the transmission not shifting into top gear? I was not
clear on that from the previous posts.

If indeed unplugging the switch restores the transmissions ability to
shift into 4th gear, what then? Can the switch then be restored and
the transmission will continue to function normally, or is this merely
a diagnostic step leading to another procedure?

Sorry to seem dense on this, but I am just "not getting" how this
whole lash-up works.