Scenario:
How on earth is it possible to switch between the camers QUIKLY without
search them manually in 3d space to activate them there or in the outliner?
and please no marker solutions!
the switching should take place while setting up the scene for time improovement!
I seriously in need for the ultimate Answer 
For a clear answer you first need a clear question. Your post is ambiguous.
Do you want to switch active camera while working in the 3d view ? The view / camera menu gives you that
Do you want to switch active camera while rendering ?
and please no marker solutions!
If the only option to either of the above is a marker solution do you want to be told that is the case or not as it is not a solution you want to hear ?
the switching should take place while setting up the scene for time improovement!
What does this mean ?
select camera press ctrl- numpad 0
or do you mean to switch between cameras without manually selecting them?
@sorry Richard Marklew! (I’m now working more than nearly 20h…little late for me - sorry for that!)
@Small Troll exactly! I want to switch between cameras(make them active) without manually selecting them! And without going to the camera menu each time…
via shortcut or something
you would need a script for that, perhaps a search through the addons foum might help. it seems such a simple thing i would be surprised if no one has done it already
thanks Small Troll. I unsuccesfully searched the add on forum for a solution.
I fear this could be the first time for me that there is no solution for a problem that I have in blender.
If it’s so it would be really sad 
I found a work around that works fine for me:
I open an aditional outliner and do only display cameras there.
After I name them properly I nearly can navigate as quick as I wanted with CTRL+num0…but a shortcut for that would be better though 
Still have to select the camera.
Pretty much same thing here.