The xyratex onestor disk shelves tend to have a mildly cursed 3.5mm TRS jack for the serial connection. No one online wanted to sell me a 3.5mm TRS to DE9 cable (despite my asking (this means I ordered that exact cable but didn't get it)). That's why I have a 2.5mm TRS to DE9 and 3.5mm TRRS to DE9 cable. The former is utterly useless, the later SHOULD work but plugging it into the shelf did nothing.
So today I was failing to hand wire, as in literally hold contacts between a double ended TRS plug and some dupont jumpers plugged into the laptop's DE9, so I decided to try and make the TRRS work. I was looking at it thinking "hmm I can get paperclips or something to jump these connections" and then thought.... what about a 3.5mm coupler?
Sure enough, with a 3.5mm TRS coupler, it works. The TRRS plugged directly in doesn't work. I swapped them back and forth again to make sure.
It's jank as fuck but it works. Job done.