The hardwired high water input on the Siren Marine devices is looking for ground. Float switches have two wires, one goes to the high water input and the other goes to ground or batt neg. When the float switch trips from the water level, the ground gets sent to the yellow wire and the Siren Marine main unit generates the alert.
Or you can pull from an existing high water alarm, which most activate with a positive voltage, in which case you would need a dc relay.
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