electrical system shutdown

Hi to all! New here been reading A LOT, nice info here. Im wondering if anyone has any info on a circuit or relay type system that will kill power to the car after the battery or system drops around 11 volts. I have seen this on Nissan, and maybe Toyota. We could leave dome lights on or door and trunks open and im pretty sure that the electrical system would shut off until you tried to start it or started messing with the light or whatever. I was told by someone that when the electrical current drops below 12 volts it activates, Im just curious, thinking that would be neat to do in my project car. Thanks for any help!

Most of the newer vehicles allow the vehicle to go to sleep after a predetermined time.  This process is not voltage sensitive.

Is it possible to wire up on a 70's vehicle?

Thank You, that should keep me busy!

Interesting project. I think there's a commercial product that does this; search for Battery Guard and a bunch of things will come up on google. If you want to DIY, the thing to use is solid state components to do the load connect/disconnect, because having a relay coil turn on defeats the purpose of the circuit. You wouldn't want the circuit to draw any extra power off the battery, either above or below your 11V threshold. It'd be easy enough to do with a voltage comparator, which then drives your transistor to turn on or off the power when the trigger conditions are met, and also bypass the cutoff when the ignition is on, to keep it from shutting down when cranking. Not much to it except to pick a transistor that will handle the current. It'd have to be a separate tap off your battery, not in line with your starter, but that shouldn't be a problem because you wouldn't expect your starter to draw anything when the car is off. The commercial item uses a mechanical latching relay that doesn't draw any power except when switching, which would be better since it could handle full current, but costs more.