I had a car dealership I was to add new servers into a new rack and recable it. I walked into a room with about half a dozen servers balanced on a pile of cat5, BNC and serial cables about 4' high. I spent 3 weeks untangling cables, removing dead cable, decommissioning serial and token ring networks and re-terminating or re-running ethernet that didn't test well.
Pretty much everything was done by scream test because nothing was marked. I found an ancient server that was still used for manuals occasionally that was drywalled into a old closet in the shop when I traced down a line I disconnected and one of the mechanics asked where his manuals had gotten to. That server was shut down every night when they turned off the shop lights and booted back up every morning for who knows how many years when someone came in to work and turned on the lights.
I eventually got to the point I could set up my rack and SANs/servers, patch everything over from the network rack I mounted on the wall, and get guys going on the workstations.
We had a series of meetings after that with the sales team about getting a technical appraisal before we sold our equipment into dealerships. And every dealership I worked in after that was pretty similiar.
Honestly, it was an amazingly satisfying feeling at the end to look in that room after I was done. I get a little shiver 20 years later thinking about it now.