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  1. #1

    Default Home built Car Alarm

    I am trying to make a system,that if the Door is opened the Car Horn Blasts.

    I have run a wire from the internal light of my 1990 Suburban though the firewall to a Toggle Switch.From one of the Horns I have run a wire to the Switch.

    The idea is that if the switch is closed and a Theif opens the the Door,the Horn will sound and the Theif will be scared away.

    However....

    I still get 12V in the wire I have spliced into the Power side of the light,even when the Light is out.Of course with the switch closed the Horn will sound continuously.I really can't work this one out.

    Thanks in advance.

    Mike

  2. #2

    Default

    The interior lights are ground switched, so you need to tap the ground wire. This will work better anyway because the horn should also be switched ground. Just connect the ground from the horn to the ground to the light.

    The problem I see though is that if you set this up, the horn would also honk every time you got in or out of the truck with that system 'armed'.

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  3. #3

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    Instead of a direct wire you would probably want to go through a relay.
    But agreed with the last poster while this may be a great poor mans alarm system it's bound to get real annoying.

  4. #4
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    Mike,
    Like Tim & PMF have said this set up will get real annoying if the horn blast everytime you open the doors to get in the truck until you can get to your switch & turn it off, but you could wire in a second switch in series so that you could disconnect the alarm from the outside switch before you open the door. It's not that much harder, just a little more wire & an extra toggle switch. The only problem is hideing it well enough so that a car thief doesn't find it.
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  5. #5

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    Quote Originally Posted by stephan View Post
    Mike,
    Like Tim & PMF have said this set up will get real annoying if the horn blast everytime you open the doors to get in the truck until you can get to your switch & turn it off, but you could wire in a second switch in series so that you could disconnect the alarm from the outside switch before you open the door. It's not that much harder, just a little more wire & an extra toggle switch. The only problem is hideing it well enough so that a car thief doesn't find it.
    When I originally repsonded, I had thought of the possibility of having a switch on the outside of the truck somewhere. It occurred to me though that personally I would be just as annoyed by having to discretely flip a hidden switch every time I got in and out of my truck as I would be by the horn.

  6. #6
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    That's true PMF & he'd also have to be aware which of his neighbors might be moonlighting as auto burglars & make sure they weren't watching when he flipped the switch Maybe a 5 second time delay box would be the ideal solution. Can you think of any automotive 12V delay boxes that he could use to apply to this? I can't think of any right now, but there have to be some.

  7. #7

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    If he were to get a bit fancier with the wiring, there is a box that uses a pulse to hold a circuit for a preset amount of time. It is generally used for diesel timers without a wait-to-start light or for opening windows or sunroofs by remote. Using that, it would theoretically be possible to have the box (which acts as a relay itself) switch an spdt relay to pin 87 to cut the ground connection. When the timer is done, the relay would return to 87A, which would allow the horns to be grounded through a relay when the light is on. This way, whenever the light comes on, it would have a delay of however many seconds the OP would want before the horn honked to be able to flip the switch. The particular box I am thinking of has an adjustable timer, and I can't remember its name, but it is made by DEI as a remote start accessory. I think you can buy them on line for around $20.

    As a side note, I like how much we are looking into this system without any further input from the OP yet. For all we know, the honking when opening and closing the door might be fine with him.

  8. #8
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    Quote Originally Posted by pmf608 View Post
    As a side note, I like how much we are looking into this system without any further input from the OP yet. For all we know, the honking when opening and closing the door might be fine with him.
    Yeah the honking might be ok if he's as deaf as I am
    I like that delay relay you described. I'm going to try & find it o. l. I can think of a lot of uses for it.

  9. #9

    Default

    Thanks alot for the replies!

    I understand that the horn Honking would be annoying,I installed a switch behind one of the Spot lights on the front where I tapped into the Wire from the Horn.The Car is parked outside my House and I am close to it all day when working.The idea of the Horn over a Car alarm was mostly that folks are accustomed to Car Alarms going off,less accustomed to continuous Horn blasts.

  10. #10

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    Quote Originally Posted by Mike Hill View Post
    Thanks alot for the replies!

    I understand that the horn Honking would be annoying,I installed a switch behind one of the Spot lights on the front where I tapped into the Wire from the Horn.The Car is parked outside my House and I am close to it all day when working.The idea of the Horn over a Car alarm was mostly that folks are accustomed to Car Alarms going off,less accustomed to continuous Horn blasts.
    Most alarms from the dealer are a car horn....if a thief ..a good one...wants your truck he will cut your horn power and have it hot wired before you can get you r phone out to call 911.

    Even with an ignition kill....which would be better.... They aren't fool proof....car alarms are only a deterent.

    Considering the time you invest in this set up a 100.00 alarm would be cheaper.


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