The systems ends up gift very, an extremely dependent top top the exact model of her car and also the physical circulation of the outlets in ~ the vehicle.
You are watching: Modifying an automotive 12v power outlet to disable power when car is off
You"ll require a business manual because that your auto that has a finish wiring diagram. Check an initial before friend buy one, as many only have actually block diagrams or step-by-step electrical tests instead of complete wiring diagram.
Next, determine the 12V outlets on the wiring diagram. Outlets that space on all the time room likely associated to B+ (straight to the battery) via a 15A fuse. Outlets that space on only with the key will be connected to a relay that will be on v the run/ignition (IGN) or accessory (ACC) key positions. It, too, will have actually a 15A fuse upstream from the outlets.
EDIT: even if your car doesn"t have switched outlets, opportunities are that it has actually something the is switched on just with the vital is in Accessory or run positions. This is where things become very model-specific. If this is a classic vehicle where the an essential switch directly controls strength to the + next of the ignition coil, affix your brand-new relay coil to that terminal. If it"s a more recent car, look very first for an IGN or ACC relay. In the unlikely event you can"t discover one, discover something that is switched on and also off v the key, and tap the strength to that machine to operate your relay. Be sure to have actually transient protection (flyback diode or snubber) on your relay coil if you execute this.
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I"d recommend including a different relay and also fuse in parallel with your currently IGN/ACC relay, then running specialized 14-12AWG cable to each DC outlet. You deserve to then install an SPDT toggle come switch between the present (always on) and brand-new (on v key) 12V supplies, v the center switch terminal associated to the DC outlet. Make sure that you usage a switch the is rated because that 15ADC or better.