using alarm aux as a fuel pump kill?

Was just brainstorming and wondering if anyone had done this before...

Would it be possible to use one of the alarm AUX outputs as a fuel pump kill switch? (this would be in addition to the starter kill) I do not know if there are any alarms that have an AUX output that isn't just a momentary circuit closure, but that could probably be used to engage and disengage a relay, couldn't it?

... just wondering if it could be done... seems like a unique idea.

If you dont want something momentary, do this:

Momentary to Constant Output
Once activated by the relay on the left, the relay's coil on the right will stay energized until either ground or 12v(+) is removed. You can do this with another relay. Or try connecting to a 12v(+) switched source instead of a constant one. Or you can have a door trigger activate a relay to break continuity. The variations are practically endless.


dont really understand what you are trying to accomplish

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Note: You Always Dont Get What You Pay For.

So if someone steal the car...can we pres the AUX button to hijack the car....So the the engine shutdown?

So what would happen if the circuit were to fail while you were driving the car? I would not recommend doing this.

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

If the circuit were to fail while you were driving, then the fuel pump would cut out and the engine would die. Not the end of the world or anything that hasn't happened before. I could understand if I were an installer doing this for someone else

People put toggle kill switches in their cars all the time, and if the wiring is solid, I don't see why this can't work just as well as one of those. I have never had a relay fail in the 11 years I've been using them. I just thought it would be a nice idea since my alarm has something like 5 AUX outputs that I'll never use (no power windows, don't have a trunk, etc.)

As for the question of whether you could use this to remotely kill the car if it were stolen, I had never thought of that, but I suppose it would work.

I will look more into that momentary to constant switch.. I had thought something like that was possible, but didn't remember how to accomplish it.

thanks!

OK, totally forgot to finish my thought.. damn phone calls. :)

Anyway, what I was saying in the first paragraph is I could understand not wanting to do it if you were installing the item for someone else and weren't sure if they would know what to do if their fuel pump were to cut out while driving, but I am the owner and only driver of this car, so I know the risks and am not worried about causing a problem.

Ist correct...To shutdown the engine while running...Immbolizer normally cut the fuel pump wire rite? If correct...we can do our own antihijack...use AUX channel to cut the fuel pump wire as a immobolizer...Anyone agree with me?

I thought about it a little more, and if you had something like this installed and someone stole the car, then they had to bypass your fuel pump kill relay anyway, so activating it would have no effect.

Unless you just forgot to engage the kill switch and they stole the car. Then it would work.

First off this would not work as a anti car jack for a couple reasons..mainly that remotes will not work when the brains recieve ignition. I suppose it can be bypassed or manipulated but you would need a spare remote at all times since the jacker would have the one on the key chain already..and range would come into play..as well as maybe getting beaten or shot/killed..not worth a car..thats what insurance is for.

If jacking is really a major concern spend the extra money for a GPS tracker unit and simply tie one of the outputs to open the fuel or ignition circuit when you enter a code thru any phone or internet..but yes it will be a bit pricey and there could be legal issues as well if when the car is stalled and it causes an accident..but don't blame me..laywers..you know, I am an installer.

As far as using the AUX output most DEI products will let you program outputs for several uses..momentary, timed, latched, validity so a relay will do it. If it is a basic unit and only has pulsed you can use a latching relay setup, very simply as well but as stated I don't really see the point.

Good Luck

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My focus wasn't to prevent carjacking, in fact I never even thought of that. I suppose if that is going to happen then you're kind of screwed anyway. I mean, how far do you want to go to protect a car that is worth $2000?

Seems like every time car thief gets into a Honda, he is thinking "gotta find that kill switch." This is just an effort to a) make it really difficult to find, and b) satisfy my inner engineer/nerd by doing it in an extremely over-complicated way just to do it.

ah ok..it seems we were over analizing this one.  Well just hide a switch in a really good spot that a thief won't find.

Cut the fuel pump wire in a hard to find spot towards the rear of the vehicle...believe me I can't imagine a thief looking that hard. Like stated earlier be extra careful with your connections as unlike a starter kill a fuel or ignition cutoff that goes bad will cause the vehicle to stall..not the safest thing at 3 in the morning friday night on a highway. If your connections are solid there is no reason to fear doing a fuel cut-off.....only those who do not know how to make a good connection would worry about failure.

Good Luck

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No need to worry here. This will be battery backed-up and all connections will be soldered and heat-shrinked. All connections and relays will be made behind trim panels so I always take the time to do them right the first time. :) I'd much rather spend an extra few hours wiring it initially than have to pull the car apart again to fix it when it fails in the future.

BTW, the alarm is a Python 900, which is a DEI product. I wasn't aware that you could program AUX outputs to be momentary or constant. That will even save me a few relays.

Yea thats one of the things I like about DEI products..they really did thier homework on the upper lines as far as vesatility and ease of programming.

Good to hear that you take the time (and pride) in your work..too many hacks out there. Do it right the first time..every time...installers creed.

Good luck and keep us posted on how it goes.

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Will do. Thanks for the help!

I'm not sure how the aux output on your alarm is set up when it's in constant mode, but it'd have to be a mechanical latching relay (which I'm guessing it isn't), or a solid state ground switched output, if you're planning on using it continuously when the car isn't running.
Otherwise you'd have a drain on the battery from the energized relay coil.

If it's a ground switched output, you can use that to ground one side of the coil of your interrupt relay, with the other side going to the ignition power. That way there's no drain when the car's off, and the relay will open your circuit if the ignition is switched on.

As reliable as your triggering circuit is, it still might be good to put a backup system in the form of a mechanical switch hidden in some out of the way place, so you can bypass it if it happens to fail.

I would imagine it would need to be configured N/C..the output programmed to "latch" , which is a negative out. Connect that to 85 of the relay. Put 86 to ignition and interupt the fuel pump through 30 and 87a.

If someone wanted to do it this way it would work fine but you would probably want to add an LED or something so you know when the latched output is on or off.

The latched output coming from the DEI unit draws no more current if on or off, it is solid state.

No problem really.

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Thought I'd bring this back up to answer it.

I did end up using the AUX channel to kill the fuel pump and it worked, but I changed it before I buttoned it back up.

Since the car already had a starter kill that I didn't want to un-engineer and change to the alarm ground-when-armed output (one of those microchip in the slot things), I just used the alarm ground-when-armed output to drive a Bosch relay that kills the fuel pump circuit. It was cleaner wiring that way since I didn't have to reverse polarity on the output, and this way I can't forget to set it when I park the car.