Cat-5 many-at-once cable identifier - simple, quick & virtually free.

[TerraHertz]

So, yesterday I added a few more cat-5 cable runs in the workshop. Usually I just mark the cable ends before pulling sets of them through cable ducts. But this time tried a different way. I wish I'd thought of this years ago.

This allows installing cable sets without any preparation or marking, wiring them randomly at one end to the wall outlets, labeling the wall outlets, then very easily identifying the cable numbers at the patch panel end to wire them to the correct patch sockets. Needs nothing but a multimeter.

I took some short (8") cat-5 patch cords, and cut them in half, giving RJ45 plugs with short cable stubs. On each one, strip the stubs sheath back a little, and bare a little of all the pairs. Twist all the solid color wires together, and all the stripe wires together.

Then on each one, solder a resistor across the combined pairs. Different resistor value for each plug: 1K, 2K (2 x 1K), 3K3, 4K3 (3K3 + 1K), etc for as many cables as you want to identify at once.
With a black marker, label each stub as 1, 2, 3, 4, etc. I only needed 4, so just used bands.

Then you just plug the appropriate stub into each newly wired outlet socket. When wiring up the patch panel, strip a few mm off any pair in each cable, and measure the resistance. Easiest with alligator clips. I'd chosen resistors with values a little above the desired value, so the reading first digit is the cable number and I could ignore the rest. Obviously, do this with no other equipment connected to the cables.

It's so stupidly simple. And yet when you google cat 5 cable identification, you get articles like this: http://www.instructables.com/id/Tracing-CAT5-Cables-with-a-continuity-tester/
Systems that rely on sending a signal down the cable require running back and forth to switch the injector to the next cable. Also batteries. And buying the injector/detector. I've never bothered with those, since pre-marking isn't that much of a nuisance.

This way, you can do all the cables (as many as you made up unique stubs for) at one sitting in the wiring closet. No battery, apart from in the multimeter, which you had anyway. It would also work for identifying previously wired but undocumented cabling.

I'm sure this must have been thought of before, and I just missed hearing of it. It's too simple to be a new thing, surely?

[free_electron]

last time i had to do this i simply plugged in all the receiving ends to the master switch ( 24 port switch )
then i plugged a small 5 port switch into one of the ports. look at the big switch which led turns on. swap port 1 with the illuminated port. tell the guy at the other side to disconnect his little switch and move to the next port. look for whihc one lights up now. swap port 2 with the illuminated one.

essentially a bubble sort algorithm. but it takes two people : one applying the labels on the wall and pluggin the portable switch in. and one at the rack swapping wires. 

i used a patch panel thet uses those keystone jacks. so i can rearrange the port order without needing to rewire. just pop em out and swap.

[TerraHertz]

Yep, I use a small switch as a debugger, when checking ports to see which ones were killed by lightning, or if cabling is broken, etc.
But your method takes two people, or a lot of annoying running around. One end of the new runs is upstairs.