I'm just reposting this information from a comment, because it took me a while to figure out how to use the switch.

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ExileAcid [author] Nov 29, 2019 @ 8:00am
@darkremor
You can use it remotely with either a keep a switch or with a vanilla keypad, you have to give it a pin number first. So make sure it has a pin. Simply enter that pin number on either the switch or the keypad. This information is also written in the town bells in game description.

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When you place the switch, among the options will be "Activate/Open Pins" and one will be "Deactivate/Close Pins." To use the switch, simply put pin codes on the items you want to toggle with the switch, and then choose one of the options and type in the pin code for that (those) item(s). If you want to activate multiple objects with the same switch, just give them all the same pin code.