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Trigger A Relay With Ground

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=142868
Printed Date: April 26, 2024 at 6:40 PM


Topic: Trigger A Relay With Ground

Posted By: goremanx
Subject: Trigger A Relay With Ground
Date Posted: April 14, 2017 at 9:26 AM

I need to trigger a relay with a ground signal. I've hooked up one end of the relay's coil to a power source, and the other end to my parking brake switch (which provides a ground when engaged). But when the coil closes the switch in the relay, it sends 12v down into the parking brake circuit and makes it hot, which I do not want.

Is there such a thing as a relay that will take a ground as a trigger for the coil, without subsequently making that ground hot? I assume it would be an electronic relay with some kind of logic built-in as opposed to a dumb mechanical Bosch relay.



Replies:

Posted By: Twelvoltz
Date Posted: April 15, 2017 at 7:12 PM
Assuming I am reading this correctly you want to prevent +12V from passing through the coil into the wire proving ground from the parking brake? A simple diode will do the trick.

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Installer, IT support, and FFL. I need less hobbies.




Posted By: goremanx
Date Posted: April 15, 2017 at 7:18 PM
I thought of that, but wouldn't a diode also prevent the dash cluster from seeing the ground when the parking brake is engaged?

I'm actually kinda confused about how the parking brake switch works in the first place. When the brake is on, the switch is closed to ground. But no actual current goes through that circuit, it's either grounded or it's not and that's how the gauge cluster knows whether to turn the parking brake light on. How is the cluster detecting a ground when no current is flowing through it? And would a diode mask the ground? It's baffling...




Posted By: Twelvoltz
Date Posted: April 15, 2017 at 7:40 PM
You do not insert the diode into the vehicle's wire. You are tapping into the vehicle's wire to activate the relay. The diode is inserted into the wire you are using to activate the relay.




Posted By: goremanx
Date Posted: April 15, 2017 at 8:50 PM
I'm confused... if I put a diode on my relay's circuit, how will the coil of the relay ever complete its circuit and energize?





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