This link contains info on the Shelly 1:
shelly.cloud
It is primarily used to control home light circuits via home automation systems like Home Assistant (which I also use). It can also operate as a relay switch for 12 VDC circuits.
If you look at the wiring diagram in the link, I connected the fuse 12 VDC hot side to an inline fuse holder connecting the 12 VDC to the "N" and "1" terminals. The "0" terminal is connected back to the F6 fuse connector feeding the HDCMM. I connected a Ground to the "L" terminal. One was available on the KIB fuse block above this fuse block. I used wire crimp connectors throughout.
Regarding the control software; I use Tasmota for my Home Assistant at my home so I used the same here. See
Shelly 1 - Tasmota
You may be able to get by with the installed app, but it may rely on having internet connectivity for the cloud app.
If you need more details let me know.
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