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Trigger A Relay With Ground


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goremanx 
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Location: Vermont, United States
Posted: April 14, 2017 at 9:26 AM / IP Logged Link to Post Post Reply Quote goremanx
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.
Twelvoltz 
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Posted: April 15, 2017 at 7:12 PM / IP Logged Link to Post Post Reply Quote Twelvoltz
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.
Installer, IT support, and FFL. I need less hobbies.
goremanx 
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Joined: April 14, 2017
Location: Vermont, United States
Posted: April 15, 2017 at 7:18 PM / IP Logged Link to Post Post Reply Quote goremanx
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...
Twelvoltz 
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Posted: April 15, 2017 at 7:40 PM / IP Logged Link to Post Post Reply Quote Twelvoltz
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.
goremanx 
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Location: Vermont, United States
Posted: April 15, 2017 at 8:50 PM / IP Logged Link to Post Post Reply Quote goremanx
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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