I had an old customer move into a new location that had been vacant for a couple of years. It had an ICC patch panel and 8-pin jacks with all wires terminated in duplex jacks at each location.
As we did the walk-through, I noted the Cat-3 wiring, but since the customer is going to use a VPN and no file-server on premise, it seemed that 10-base-T would be doable on Cat-3 without running new cable.
The building had an ample crawl space with visqueen on the floor and all the greenfield ran down. The patch panel was mounted on an outside wall about 6 feet off the floor, a single gang old-work box turned sideways, and everything appeard O.K.
After the KSU, VM, and 7 phones, and the 3 outside phone lines were ordered, I got my first surprise. The customer wanted to add two desks in a room that had outlets with no cable. No problem, that's an extra. I grabbed my 4 boxes of wire, fish tape, green sticks, flashlight and ladder and headed for the crawl space.
Upstairs, I taped a voice and data cable to my tape and pushed them down into the crawl. I took the green sticks and I could feel the plate on the wall under the patch panel, so this should be a piece of cake!
Oops, the idiots had actually stuffed 14 cat-3 cables in a 3/4 inch greenfield, run through a single gang box on the way to the patch panel, and, of course, since I was not supposed to do any crawl space work, my right angle drill was in the warehouse. Well, no matter, I installed the phone system and set 5 phones up and saved the data and crawl space work for the next day.
I get all my new cables in, set the last 2 phones and test the new jacks and everything is great. Now to map the rest of the jacks.... I plug my tester in and it indicates split pairs on pins 3-4-5-6.
All 16 existing jacks were wired straight color code 1-8! I guess it had never been used for data and the phone system didn't mind the split pairs when the longest cable was 60 feet. The jacks were the ICC tool-less Insulation displacement (the cap cinches the wires) and there is no wire guide on the jack. I guess the installer didn't know that you have to apply a T-568 A or B to the pins.
Sigh, time to rewire BOTH ends.
Fortunately, I only had to rewire 6 jacks. I left 2 locations on voice pair split and am going to install 4 data cables on one side of the room at a later date.
If anybody wants to know, you peel off the wires on 1-5, move the white green to pin 3, move the orange pair to 1&2, and turn the blue pair over and put them on 5&4.
Piece of cake :-)