I have a functioning EISY system with a 2413S PLM. The upgrade website indicates that I need a serial PLM kit:

https://www.universal-devices.com/product/serial-plm-kit/

I already have some type of cable system to the PLM that is working:

Do I need to get the serial PLM kit?

It would seem "No" you don't need the Serial PLM kit.

You may already be using a USB-to-Serial adapter from elsewhere, and if it's working and your PLM is happy, that's fine. You state that you have a working system, and any upgrades from here on should be software-only for you.

(it's hard to be completely certain from your photo and wiring, but it seems your translucent-blue USB plug and associated sliver-braided-clear cable at the top right of your photo is a USB-to-serial adapter. There are many such adapters floating around, and it's good if you have one that is working. From the blue DB-connector, you have what seems to be a beige DB-connector to RJ-45 adapter. If this is working, and provides your PLM with the needed signals, then it would seem you are good-to-go).

Edited 18 hours ago18 hr by GPritchard

Thank you. Yeah, that is where I put the system when it was having a hard time with Zwave. This puts it in the middle of the house, so it works better.

The system does work (until I tried to upgrade the software anyway).

I'll keep it as is.

Straying off-topic here 😁

I wonder if your Z-Wave coverage would be improved if you remote your UD Dongle?

I found that was the case: I used a USB-A male to USB-A female extension cable, about 5ft long, and it seems to work fine:

Oh yes, higher up usually means better communications.