Stereo on key off

When the coil of an SPDT relay is at rest, or not energized,  terminals 87a (normally closed) and 30 (common) have continuity.

Initially, when you turn on the key to the accessory position, the first relay becomes a latch and continues to supply 12V+ to the radio's accessory lead even after you turn the key to the off position. Once a door is opened with the key in the off position, the coil of the second relay is energized and ground is broken to the coil of the first relay (latch). Now the first relay no longer supplies 12V+ to the radio. Once this happens, the only way for the first relay to supply 12V+ to the radio again is by turning the key to the accesssory position again.

the12volt • Support the12volt.com

The third relay in my diagram is needed to prevent the radio, or whatever you have the set up powering, from turning off when you open a door with the key in the accessory and run positions. 

the12volt • Support the12volt.com

LittleBill wrote:

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....once i turn the key to on or  acc, the whole relay setup would get bypassed and the radio would get power regardless because u aren't cutting the wire, ur just splicing into it and adding an additional power source? correct me if im wrong, and my other question where are u getting 5 post relays, i have looked a couple places like radio shack they only have 4 post ones

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Look at the diagram again, you are cutting the wire to the radio That's what the dashed line indicates. You can purchase SPDT (5 posts) relays from a local electronics shop or on line. You can also call Eagle Parts at 800-726-5930 Monday through Friday 8:00 AM - 5:00 PM CST.

the12volt • Support the12volt.com

LittleBill wrote:

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actually i have to ask another question, if u want to cut power to everything but the radio couldn't u just put a diode before ur splice inline to the radio? that way power can't run backwards? through the accessory line? wouldn't that be all u need to do or am im completly missing something

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Yes and no. You would have to use a diode with a rating high enough to safely pass the current draw of the radio without destroying the diode. If that is what you want to do, I'd still use relays and one amp diodes to power the radio while isolating it from anything else you want to run on the same lead, but my answer is limited and depends on what you mean by everything.  If you describe exactly what it is you are trying to do,  I'll do my best to describe what you'll need to do to accomplish it.

the12volt • Support the12volt.com

well i got my relay circuit does sell them but they are 12.99 13.77 with tax, this is high although it does come with the socket and 14 gauge wiring part number is 525t but if u just need the realy which is really all i needed its 610t, i will post my results later