DIYer seeks help finding and connecting a voltage control relay

This $4 relay can be adjusted for turn on voltage and on/off hysteresis.....

https://www.aliexpress.com/i/4000014371546.html

THanks...  Looks promising. I don't think I understand how to wire it and the diagram isn't so clear.  Any thoughts on that?

I assume the green terminal block is the relay - connect the normally open pair of pins in series with your pump. The normally closed pin wouldn't be needed.

The pins for the other 2 connectors are marked under the card.

I assume one is for the DC power to run the circuit on the card and the other is the control voltage.

In your case I think they can be the same voltage - your battery voltage.

I think that would mean you connect V to V to your battery positive and G to G to battery negative.

I am not sure what the middle pins are for, but they may not be needed.

Adjust the hysteresis to 1 volt or whatever works better.

Adjust the threshold to 12 V.

If the threshold is ratiometric, the voltage to the detection circuit may need to be constant. This gets more complicated - you would need a regulator on the circuit supply voltage and ensure the threshold voltage is in the correct range for this supply.

Check around or ask the supplier for a more complete data sheet or application notes.

THanks so much for the detailed help. It's the inverter that should get turned off by this, I think -- so would I connect to the inverter switch as you outlined? 

Yes the relay can turn off the inverter.

  Hello again Mr. Wong.  Here is what I have, and I want it to control  my inverter, turning it off when the power in my (solar charged) battery dips below 12v.  Can you tell me exactly how to hook this up?  Right now the battery is connected to two terminals at the back of the inverter.  I assume that I should attache the power supply cables marked above to those terminals.  But then which of the terminals do I use for the switch wires?   Thanks so much if you can help with this.

  Hello again Mr. Wong.  Here is what I have, and I want it to control  my inverter, turning it off when the power in my (solar charged) battery dips below 12v.  Can you tell me exactly how to hook this up?  Right now the battery is connected to two terminals at the back of the inverter.  I assume that I should attache the power supply cables marked above to those terminals.  But then which of the terminals do I use for the switch wires?   Thanks so much if you can help with this.