I can’t draw well. So i use plantUML.
There is a example: link
No schemes here. To be able to maintain the cable salad I had switched from the diagrams to simple org-mode tables. They are structured by the main interconnection boxes. It’s easy to update any changes. When re-wiring the studio I can easily follow the cables even if it looks like a mess in the end. Label stickers on audio and MIDI patchbays keep the use sane. Only the MIDI I/O cables are labeled with stickers (IN/OUT) and only the black ones.
Thanks for that link @tralivallo, that codeuml site’s pretty great.
@cube48 Good Lordy! That’s some thick dense pasta. I’m amazed by your patience and logic.
I made one with Gliffy in 2014, its pretty big but i think its interesting to look at.
The PDF is under here
@Kites, yes, patience is needed 
It takes usually one whole day to disconnect, clean/remove/add some bits and patch everything together. It’s not funny job but that documentation makes it quite easy to follow the connections.
Patchbays (audio and MIDI) are double-sided swords, they give you enormous flexibility and ease of use but they double the amount of cables.