Turn +12volt on only when ignition off

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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=50143
Printed Date: July 19, 2025 at 3:16 AM

Topic: Turn +12volt on only when ignition off

Posted By: Newtyp
Subject: Turn +12volt on only when ignition off
Date Posted: February 15, 2005 at 8:58 AM

Hello,

I believe that this would be possible, but I am completely dumbfounded on how to wire it together. Please advise.

I am trying to have a relay or maybe there is something else that can do the trick that could be recommended that turn a lead into +12volts once the car ignition is turned off. Similar to the VARAD Led alarm lights, once the ignition is turned off the lights flash.

I tried to search on the forum but have had no luck. I am trying to wire a shock sensor for my fathers Acura TL due to the increased HID thefts in the area however I do not want the shock sensor to be on at all times, only when the car is off. Please advise.

Thanks

Ken

Replies:

Posted By: Velocity Motors
Date Posted: February 15, 2005 at 11:14 AM

Use a relay SPDT :

86: Ground
85: 12 volts switched
87: NOT USED
87a: 12 volts constant
30: This will go to the (+) side of the device that you want to have turn on when ignition is OFF

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

Posted By: Newtyp
Date Posted: February 15, 2005 at 11:17 AM

Jeff,

Thank you for the FYI. I will give it a try later today.

My best regards.

Ken

Posted By: hotwaterwizard
Date Posted: February 19, 2005 at 12:36 AM

Here is a drawing of the Relay inside view and connections.

posted_image

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !