special relay idea needed

Printed From: the12volt.com
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=116151
Printed Date: May 19, 2025 at 6:00 AM

Topic: special relay idea needed

Posted By: jamoman
Subject: special relay idea needed
Date Posted: September 07, 2009 at 9:50 AM

I would like to make a device that I can have a circuit active only when my ignition is on, but it has to be initiated by a momentary switch, which then allows the device to be active when the ignition is on. Here's the procedure to activate it:

1. Hold the momentary switch in the "on" position
2. Start the vehicle
3. Let go of momentary switch and device stays active
4. Device stays active until ignition is turned off.
***Actions 1 to 3 required again to activate the item.

Can anyone tell me how to make this work with relays or ???

Thanks for your help

Replies:

Posted By: i am an idiot
Date Posted: September 07, 2009 at 10:05 AM

https://www.the12volt.com/relays/page5.asp#lsp
You will have to substitute the wire labeled Constant 12 volts (In the picture) With a true ignition source. You will have to turn the key to the on position before you press the momentary switch. The relay will then stay on through the start cycle and remain on until the ignition switch is turned off or the switch is pressed again.

Posted By: jamoman
Date Posted: September 07, 2009 at 2:04 PM

Fabulous, thanks!

Posted By: howie ll
Date Posted: September 08, 2009 at 2:12 AM

Amazingly we call this device an accessory lead.

Posted By: i am an idiot
Date Posted: September 08, 2009 at 3:51 AM

You have to use a True Ignition source to power this apparatus. An accessory wire loses voltage during a start condition. A true ignition is hot when the ignition is ON and it is still on during the start cycle.