I ran into a weird one today. House I'm working at has phone service from cable company. Everything is wired with quad wire, but it's mostly all in good shape. Only a single line, so nothing on yellow/black anyway. About 4-500 feet from the house is the barn. There is an existing buried phone cable from the house to the barn, standard sort of direct burial, metal rodent shield, icky pic sort of thing. Not twisted pair, but normal quad colors.

The barn feed was already tied into the house wiring using the yellow/black wires. In my brain this meant there was probably a fault on the red/green. I slap up a couple cheap wall phones in the barn and horse arena and they seem to work fine. (To be fair, I heard dial tone and called it a win, because I was too busy with 100 other things going on. Well, I had some dead time tonight when I was there and called a friend to kill some time while waiting on some stuff to show up. Cell service is lousy at this house, and since I'm friends with the owner, I jump on the house phone. Then I hear it. That godawful sound of an unbalanced line. Argh.

So, I poke around. Clip the scotchloks off the line going to the barns and what do you know, nice and quiet line. OK, so there's some issue with a buried cable that's who knows how old... shocking.

So I try using the red/green pair.

Same result.

Try weird combinations, red/yellow, red/black, green/yellow, green/black

Same result. Noise.

I don't know what the heck possessed me to try the next thing....

I parallel the wires. Inside the house I hook ring to Red+yellow and tip to Green+black..... The far end is still only connected to the yellow/black at this point.

The line is DEAD SILENT. Not dead, it works perfectly and has no noise.

I'm stumped. It works, hooray. I'd love to know why.