power supply - how to build a low-voltage disconnect switch for DC 12.4V 70A?

How can I make a device that will make the power connected as long as the voltage of the power-supply keeps over 12.4 V (adjustable) and disconnect it if it falls below?

It also must connect the power back, but only if it rises above 13.5 V.

This has to sustain at least 70 A.

Is there a simple way to build such device?

Answer

70A power relay and voltage comparator with a transistor to run the relay.

Here's a schematic:

Use this link to simulate it.

You'll need to tweak the values to get it how you want, I didn't perfect it.