I need a simple schematic for a circuit that when the dc voltage in is higher then 13 volts dc the circuit lets it pass through then when the voltage drops below 13 volts it does not pass through, then if the voltage rises to above 13 volts dc again it lets it pass through.
I did a circuit on the Grid tie inverter thread a few days ago thats a type of voltage latching window switch. It may be more than what you are looking for. but it shows a basic two step voltage comparator circuit. You may only need one side of it.
"on the input line" do you mean: put the zener diode on the positive line pointing to the out or crossing gnd with positive with the zener pointing to positive
Suppose your input line is like a piece of hose with a nozzle on the end. This will make it clear to explain. Cut it with a knife. Put a zener in the cut so that the line on the zener (the cathode lead - k) goes towards the nozzle.
Any voltage above 13v will appear at the nozzle.