Let me reply to my own posting to document how this all worked out.
While there was no response on the forum, Mike did immediately respond when asked directly, thanks!
It turns out that OUT0 is "hard coded" to do the Connect function when using mode 14 (Elecraft twin). You can set OUT1 and OUT2 any way you want (duplicating the Connect function, if you want), but OUT0 is always Connect. Hence, it is not possible to free it up; it is possible to set OUT2 also as Connect but I would lose one OUT port which is not what I wanted.
I "solved" the issue by making a small cut in the cable going tot the I/O connector and using that to splice off the OUT0 signal for the K3 DB15 connector.
Not entirely clean but I was able to make a reasonable solution with some heat shrink tube and I made my own cables anyway.
However, I was still able (using the same I/O cable) to get access to OUT1 and OUT2 and use them to "switch something else". Each of those now drive a solid state relay (Carlo Gavazzi RP1A23D5, but there are many alternatives) and I can switch-on and switch-off power supplies and the like at the radio location to save energy, which was the original plan.
(I need the I/O connector for that because the OUT outputs switch to ground and I needed the 8V output to drive the solid-state relay between).
I also made another "electrical power switch box" that uses the 12V DC output of the K3 to switch more stuff. Now, OUT1 and OUT2 switch some parts of the remote station and my transverters et all power-up if the K3 is switched on.
While I would have preferred to use the PAD port for K3 power control, the issue is minor and at the remote radio end. So it goes,
Geert Jan
