• 4 Posts
  • 9 Comments
Joined 4 years ago
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Cake day: August 30th, 2020

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  • 85 needs to be connected to 12v, not ground.

    I think you may have just solved my problem. When I’ve used relays in the past, pin 85 was connected to ground, since I wanted the relay to close when the trigger went high. I’m not sure why it never occurred to me that I’m essentially trying to do the opposite thing here, since the horn is triggered when the trigger wire is connected to ground.

    I’ve never worked with individual diodes, so I’m not sure about the correct terminology, but which way would I want the diode to “face”? Do I want it to allow current to run from the 12V source, through the added relay, to the horn switch wire, or the other way around?

    Additionally, would I need to add an in-line resistor? It makes me a little nervous connecting the horn switch to 12V, given that I doubt it’s designed to carry a significant amount of current.






  • This coil has a standard resistance/impedance

    I see. I was under the impression that there’s a seperate resistor to avoid shorts when you connect from the trigger to ground.

    What year/model of car?

    It’s a 2014 Nissan Altima. I’ve spent quite a bit of time trying to find wiring diagrams, but I haven’t gotten very far. I got to the point I’m at now by following some old forum posts and confirming with a multimeter. What you described sounds accurate: the horn wire under the steering column seems to always be at 12v. Pressing the horn seems to send it to ~0V, so I assume it’s just jumping to the shared ground wire. I will say that when I disconnect to horn at the front of the car (to silence it), I can hear a relay in the engine bay clicking when I press the horn. I figure that implies it’s a physical relay, rather than a computer somewhere.

    And realistically you could in a pinch pull coil power from the horn itself

    This is something I’ve considered doing. The circuit I’m adding with the relay is extremely low current, so I don’t think it would be too tricky to run wires from a relay connected right next to the horn to the cabin. I can just ground the relay to the frame of the car right near the horn such that there’s minimal chance of creating a short on the high-amp horn circuit.